Mecha Skirmish Packet snapshot 2026-09-05

Full rules with IDs. The styled edition has the pipeline, hit-band and line-of-sight diagrams.

Mecha Skirmish Rulebook

Draft v0.3 · 2026-09-05 · hex grid · 3v3 · best of three

Working ruleset for a digital, competitive, hex-grid mech skirmish. Rules carry IDs like sprue parts (A1, F4) so review comments can point at one exactly. Every number in a table is a starting value to tune, not a commitment.

A styled version with diagrams is in rulebook.html (open locally) and as a review artifact at https://claude.ai/code/artifact/e3269bf1-5f54-42bd-bd04-01a88b2be811. The simulator in this repo implements these rules; engine/*.ts cites rule IDs in comments.

Status legend: Locked decided in discussion · Proposed recommendation that needs a yes · Open undecided, parked · Example placeholder content or numbers.

A. Pillars & vocabulary — Locked

  • A1 Every resolution is a visible die. Hit, location, penetration, damage, initiative, stress, falls: each is a physical die rolled on the table. Modifiers are dice too (F2), never hidden percentages.
  • A2 Building a roster is a small number of real decisions. Enough depth for a metagame, never a monumental setup task. Exact count to be revisited once the part catalog exists (K).
  • A3 Damage lands on parts, not on a health bar. Where a shot hits is decided by part size; what it does is decided by that part's armor and durability. Losing an arm loses a weapon. Losing legs loses mobility.
  • A4 A game ends in about twenty minutes. Alternating activations, a round cap, and objectives that force contact.
  • A5 Vocabulary
    • Roster: your four mechs. Three are fielded, one is the sideboard.
    • Kit: a chassis sold with a complete default build and a suggested pilot.
    • Runner: one manufacturer's sprue sheet. Runners share their five names with pilot factions.
    • Part: anything clipped from a runner: Chassis, Head, Arm, Legs, Back.
    • Mech: six parts plus a pilot.
    • Activation: one mech's turn. Round: all six mechs have activated once.
    • Game: one board to a result. Match: best of three games.

B. Roster building — Locked structure · Open total choice count · Example weights

  • B1 A roster is four mechs. Three are fielded in a game. The fourth is the sideboard (I2).

  • B2 A mech has seven slots: Chassis, Head, Right Arm, Left Arm, Legs, Back, Pilot. Every slot must be filled. Arms are weapons or shields; there is no separate weapon layer. Back is a single mount. Internal systems live on Head and Back parts.

  • B3 Weight. Every part has Weight; pilots weigh nothing. A mech's Weight is the sum of its parts including the chassis and may not exceed its class cap. The three fielded mechs together may not exceed the Team Cap. A sideboard swap must leave the team legal.

    Class Mech cap Note
    Light 35 Fast, fragile, cheap
    Medium 50 Baseline
    Heavy 65 Slow, armored
    Team Cap 145 Three full Mediums fit (150 does not). Heavy + Medium + Light fits. Two Heavies never fit.

  • B4 Overload. A mech may exceed its class cap by up to 10 Weight. Each 5 over, or part thereof, costs 1 Speed and 1 Evasion. The Team Cap is hard.

  • B5 Copy limits. At most two copies of any part across the four-mech roster. Each pilot is unique. Chassis count as parts.

  • B6 Kits. Every chassis ships as a kit: all six parts pre-chosen and a suggested pilot. A roster of four untouched kits is legal and meant to be viable. Any part may be swapped for any part of the same slot from any runner. Cross-runner builds carry no penalty.

  • B7 The sprue is the build screen. Parts hang on their runner by gates; clipping a part snaps it to the frame. A part's physical size on the runner is its Size stat, its share of the hit table (F4). Unused parts stay on the runner; the fourth frame sits on the sprue as the visible sideboard.

  • B8 Open. Whether 7 slots × 3 mechs is already too many decisions is parked until the part catalog is drafted. Kits keep the floor at four choices regardless. Candidate reductions: merge Head into Chassis, or make Back part of the Legs choice.

C. Stats & parts — Locked Lancer baseline · Example numbers

Lancer's Everest is the reference frame: Size 1, Armor 0, HP 10, Evasion 8, E-Defense 8, Speed 4, Sensors 10, Heat Cap 6. Our chassis bracket those values so the d20 hit math (F3) lands near Lancer's feel: a competent pilot hits a baseline target about 70% of the time.

  • C1 Chassis carries the core (the part you must destroy) and the baseline stats.

    Class Core Dur Core Armor Core Size Evasion Speed Sensors E-Def Reactor Weight
    Light 12 4 5 11 5 8 9 5 8
    Medium 18 6 6 9 4 8 8 6 12
    Heavy 24 8 7 7 3 7 7 8 16

  • C2 Every part has Size (share of the hit table), Armor (the number a penetration roll must reach), Durability (damage before destroyed), Weight, plus whatever it modifies.

  • C3 Arms are the weapons. Weapon stats: Range (hexes), Shots per Fire, Acc (added to the hit roll), Pen (added to the penetration die), Damage dice, Heat per Fire, tags.

    Arm Runner Range Shots Acc Pen Dmg Heat Size Armor Dur Wt Tags
    Rifle arm Kessler 8 1 +1 2 2d6 1 3 5 8 7
    Autocannon arm Kessler 6 3 0 1 1d6 2 4 5 10 10 Burst
    Cannon arm Nine Suns 12 1 −1 4 3d6 3 4 5 9 13 Heavy
    Blade arm Hollow Saints melee 1 +2 3 2d6+2 0 3 6 10 8 Melee
    Shield arm Nine Suns — — — — — 0 5 9 14 11 Guard
    Pulse arm Tessellate 6 2 +1 0 1d3 1 3 4 7 6 Each hit adds 1d3 Heat to target

    Tags: Burst shots resolve one at a time. Heavy 1[−] if the attacker moved this activation. Melee adjacent only, ignores cover and Engaged, may reroll location once, rolls Piloting to hit (F11). Guard enables the Guard action (E5) and the shield's melee rules (F11.6).

  • C4 Legs

    Legs Speed Evasion Size Armor Dur Wt Note
    Standard legs 0 0 5 5 12 9
    Light legs +1 +1 4 4 9 6
    Heavy legs −1 −1 6 7 16 13 Raises class cap by 10
    Jump legs 0 0 5 4 10 10 Ignore elevation costs (H3). +1 Heat in any activation you climb

  • C5 Heads

    Head Size Armor Dur Wt Modifies
    Standard head 1 4 4 2
    Targeting head 2 3 4 3 Acc +1 on all attacks
    Armored head 1 6 6 4
    Sensor head 1 3 3 2 Sensors +3, E-Def +1

  • C6 Backs

    Back Size Armor Dur Wt Effect
    Missile rack 2 4 6 8 Weapon: Range 10, Shots 2, Acc 0, Pen 2, 1d6+1, Heat 2. Indirect: may fire without LOS at a Locked target at 1[−]
    Reactor booster 2 4 5 5 Reactor Cap +3
    Sensor mast 2 3 4 4 Sensors +2. Lock On is a free action once per activation
    Smoke launcher 2 4 5 5 Quick: place a 3-hex smoke cloud within 6 hexes. Soft cover until end of next round
    Bare back 1 4 3 0 No effect; keeps the Back band non-empty

  • C7 Derived mech stats

    • Evasion = Chassis Evasion + Legs Evasion + Pilot Piloting − overload penalty (B4)
    • Speed = Chassis Speed + Legs Speed − overload penalty
    • Sensors = Chassis + Head + Back Sensors
    • E-Def = Chassis + Head E-Def + Pilot Systems
    • Reactor Cap = Chassis Reactor + Back Reactor
    • Accuracy of an attack = Pilot Gunnery + weapon Acc + Head Acc
    • Hull = sum of Durability of all six parts (display only; death is core death, F7)
    • Hit table = the six parts' Sizes scaled to 20 bands (F4)

  • C8 Example kits (weight includes chassis; card stats exclude pilot modifiers)

    Kit Class · Runner Parts Wt Eva Spd Sens E-Def Reactor Hull Pilot
    Courier Light · Meridian Light legs, Rifle arm, Pulse arm, Sensor head, Sensor mast 33 12 6 13 10 5 43 Vex Adair
    Foreman Medium · Kessler Standard legs, Autocannon arm, Rifle arm, Standard head, Missile rack 48 9 4 8 8 6 58 Ilse Brandt
    Reaver Medium · Hollow Saints Jump legs, Blade arm, Autocannon arm, Targeting head, Smoke launcher 48 9 4 8 8 6 57 Ruko Han
    Bastion Heavy · Nine Suns Heavy legs, Cannon arm, Shield arm, Armored head, Reactor booster 62 6 2 7 7 11 74 Sato Ren

    A Team Cap of 145 fits Courier + Foreman + Reaver (129), or Bastion + one Medium + Courier (143), but not Bastion + two Mediums (158).

D. Pilots — Locked two-axis synergy, bonds, cosmetic decoration · Example pilots

  • D1 A pilot has four stats, each 0 to 3: Gunnery (attacks), Piloting (Evasion), Systems (E-Def, Lock On), Initiative. Pilots are pre-built.

  • D2 Every pilot has a Faction and a Specialty. Factions: Kessler Yards, Meridian Circuit, Hollow Saints, Nine Suns, Tessellate. Specialties: Striker, Vanguard, Marksman, Operator, Engineer, Scout.

  • D3 Additional Ability. Each pilot has one passive that is only active if at least one other fielded pilot shares their Faction or their Specialty.

  • D4 Bonds. While two bonded mechs are within 2 hexes of each other, each gets 1[+] on attacks. A bonded pilot may use the Backup Fire reaction (E6): when your bond partner attacks a target in one of your weapons' range and LOS, fire one shot from that weapon at 1[−].

  • D5 Decorations are cosmetic only: kill marks on the mech, medals on the pilot card. Nothing about a pilot changes between matches.

  • D6 Example pilots (Gunnery / Piloting / Systems / Initiative)

    Pilot Faction · Specialty G/P/S/I Ability Bond
    Ruko Han Hollow Saints · Striker 2/1/0/2 After moving 3+ hexes, your first attack this activation gains 1[+] Marrow
    Marrow Hollow Saints · Vanguard 1/2/0/2 When a hostile ends a move adjacent to you, reaction: one melee attack at 1[−] Ruko Han
    Vex Adair Meridian Circuit · Scout 0/2/1/2 At round start, allies within 3 hexes gain +1 Speed this round Ilse Brandt
    Ilse Brandt Kessler Yards · Engineer 1/0/2/2 Stabilize also restores 1d6 Durability to one part that is not destroyed Vex Adair
    Sato Ren Nine Suns · Marksman 3/0/1/1 Aimed Shot has no 1[−] Q
    Q Tessellate · Operator 0/1/3/1 A target you Lock On also suffers 1[−] on its own attacks until end of round Sato Ren

    Fielding Ruko, Marrow and Vex switches on Ruko and Marrow (shared Faction) but leaves Vex dark. Swapping Marrow for Q turns everyone off. The math of who lights up is the roster puzzle.

E. Rounds & activations — Locked alternating activation, action list, no facing · Locked (preliminary) round cap 7

  • E1 A game is at most 7 rounds (preliminary; revisit once terrain and zones are simulated). Each round: roll initiative, alternate activations until all six mechs have acted, then score zones (I4).
  • E2 Initiative. Each player rolls 2d6 + highest Initiative among their fielded pilots. The winner chooses who activates first. Ties reroll. Players alternate one mech at a time; a player with no mechs left to activate passes and the other finishes their remaining activations.
  • E3 Activation. Move up to Speed in hexes, split however you like around actions, plus two Quick actions or one Full action. Free actions are unlimited. One Reaction per round.
  • E4 Quick actions
    • Fire: attack with one arm or the Back weapon (F). Add its Heat. Once per activation (Barrage is the only way to shoot twice).
    • Boost: move up to Speed again.
    • Lock On: pick a hostile within Sensors range and LOS. Roll d20 + Systems ≥ target E-Def. Success: the target is Locked until the end of the round. Everyone gets 1[+] against a Locked target; Indirect weapons may fire at it without LOS.
    • Brace: all your parts get +1 Armor until your next activation. You may not Boost this activation.
    • Vent: clear 1d6 Heat.
    • Strike: one improvised melee attack, once per activation, separate from Fire (F11.1).
    • Throw: while grappled, a contest to drop the other mech Prone (F11.5).
  • E5 Full actions
    • Barrage: Fire two different weapons. +1 Heat on top of their costs.
    • Aimed Shot: Fire one weapon with Shots 1 and choose the location band instead of rolling it. 1[−].
    • Overwatch: name one weapon. Until your next activation you may spend your Reaction to Fire it at the first hostile that ends a move in its range and LOS.
    • Charge: move and strike with momentum, pushing the target (F11.3).
    • Grapple / Break: start or end a grapple (F11.5).
    • Stabilize: Heat to 0, remove one crit effect, stand up if Prone.
    • Guard (Shield arm): one adjacent ally has hard cover against attacks coming from your side of them until your next activation.
  • E6 Reactions (Locked 2026-09-05). Each mech has one Reaction per round, reset at round start. Reaction attacks take 1[−] except Overwatch. A Prone mech cannot react.
    • Overwatch shot: the held weapon Fires at the first hostile that ends a move in its range and LOS (E5).
    • Backup Fire (D4): when your bond partner attacks a target in one of your weapons' range and LOS, one shot from that weapon.
    • Disengage strike: when a hostile adjacent to you moves out of adjacency, one melee attack against the hex it left (F11.8).
    • Pilot reactions: Marrow's riposte, a melee attack when a hostile ends a move adjacent to him (D6).
  • E7 Engaged. Adjacent hostiles are Engaged. An Engaged mech has 1[−] on ranged attacks. Melee ignores it.
  • E8 Facing: none (Locked 2026-09-05). Mechs have no facing. Position, range, elevation and cover are the only geometry that matters. Flanking is expressed through cover and zones, not arcs.

F. Combat — Locked pipeline, size-weighted location, per-part armor, dice, thresholds, crit tables, melee (F11)

Per shot: Hit → Location → Penetration → Damage. Every shot of a multi-shot weapon runs the whole chain on its own.

  • F1 Declare. Choose a weapon and a target you have LOS to (H4) within range. Optimal range is up to the weapon's Range. Long range is up to 1.5× Range, rounded down, at 1[−]. Beyond that, no shot. Melee needs adjacency.

  • F2 Modifier dice. Collect every [+] and [−] that applies. They cancel one for one. Roll the remainder as d6s and take the single highest: add it for [+], subtract it for [−]. Roll once per Fire action and apply to every shot in it.

    Accuracy [+] Difficulty [−]
    Attacker at least 1 level above the target Soft cover: 1
    Target is Locked Hard cover: 2
    Bond partner within 2 hexes Target moved 3+ hexes in its last activation: 1
    Target did not move in its last activation Attacker is Engaged and firing a ranged weapon: 1
    Pilot abilities (D6) Long range: 1 · Heavy weapon after moving: 1 · Aimed Shot: 1 · Indirect fire: 1

  • F3 Hit. Per shot, roll d20 + Gunnery + weapon Acc + Head Acc ± modifier result. Hit on Evasion or more. A natural 20 always hits and adds +1 to that shot's penetration roll. A natural 1 always misses.

  • F4 Location. Per hit, roll d20 on the target's silhouette. The six parts' Sizes are scaled to 20 bands by largest-remainder rounding. A standard Medium reads Head 1, Right Arm 2–4, Left Arm 5–7, Core 8–13, Back 14–15, Legs 16–20. A Bastion (sizes 1/4/5/7/2/6, sum 25) scales to Head 1, Cannon 2–4, Shield 5–8, Core 9–14, Back 15, Legs 16–20.

    • Band belongs to a destroyed part: the hit transfers to the Core (penetration vs Core Armor).
    • Band belongs to a part behind hard cover (H5): the shot hits the cover. It is over.
    • Aimed Shot chooses the band. Melee may reroll the location die once.

  • F5 Penetration. Per hit, roll d6 + weapon Pen (+1 on a natural 20 hit) against the struck part's Armor (Brace adds +1).

    Result Effect
    Below Armor Glance: half damage, rounded down
    Armor or more Full damage
    Armor + 4 or more Full damage and a crit: roll d6 on the part's crit table (F8)
    Natural 6 on the die Always at least Full

    With these numbers a Rifle (Pen 2) gets Full on a Medium arm (Armor 5) two rolls in three, and on a Heavy core (Armor 8) one roll in six. The crit margin was 3 in the first draft; the simulator showed the Cannon (Pen 4) critting on 53% of its hits, so it moved to 4 (decided 2026-09-05).

  • F6 Damage. Roll the weapon's dice and subtract from the struck part's Durability. Anything past 0 carries into the Core with no second penetration roll. A part at 0 is destroyed (F7).

  • F7 Part destruction

    Part destroyed Effect
    Head No Lock On. 1[−] on all your attacks. Head modifiers are lost
    Arm That weapon or shield is gone. Guard ends
    Legs Speed halved (round down). Evasion −2. No Boost. Further leg hits transfer to the Core
    Back Its weapon or effect is gone. Reactor Cap loss can push you over cap immediately (G2)
    Core Mech destroyed and removed. Pilot survives (cosmetic)

  • F8 Crit tables (Locked for v0, tune by simulation), one d6 per crit. Effects last until removed by Stabilize.

    d6 Arm Legs Head Back Core
    1–2 Jammed: cannot Fire next activation Gyro hit: Prone Sensors scrambled: no Lock On Offline until Stabilize Reactor breach: +1d6 Heat now
    3–4 Actuator: 1[−] with this arm Actuator: Speed −2 Optics: 1[−] on all attacks Offline until Stabilize Structure: Core Armor −1 for the game
    5–6 Ammo cook-off: arm takes +1d6 Knockdown: Prone, movement ends Pilot shaken: lose one Quick next activation Destroyed outright Ammo cook-off: Core takes +2d6

  • F9 Prone. Evasion −3. Standing costs your whole Move, or is free with Stabilize. Melee attacks against a Prone target may reroll location twice.

  • F10 Order of shots. Resolve each shot fully before the next. Between shots the attacker may not change target.

  • F11 Melee (Locked 2026-09-05; numbers are placeholders). Every melee attack needs adjacency, ignores cover and Engaged, may reroll its location die once, and rolls Piloting instead of Gunnery for the hit (head and weapon Acc still apply).

    • F11.1 Strike (Quick, once per activation, separate from Fire). Every mech has two improvised strikes. Punch needs an intact arm; a Shield arm punches at +1 Pen. Kick needs intact legs; if a kick misses, the kicker rolls d20 + Piloting and falls Prone below 10.

      Strike Acc Pen L / M / H Damage L / M / H
      Punch 0 1 / 2 / 3 1d6 / 1d6+2 / 2d6
      Kick −1 1 / 2 / 3 1d6+2 / 2d6 / 2d6+2

    • F11.2 Melee weapons (the Blade arm) are Fire actions with the melee rules above.

    • F11.3 Charge (Full). Move up to Speed, at least one hex, ending adjacent to the target, then make one melee attack (strike or melee weapon) with 1[+] per 3 hexes moved, max 2. On a hit the target is pushed one hex directly away; if that hex is blocked, occupied, off the board or more than one level up, it takes 1d6 to the struck part instead, ignoring Armor. A push over a drop of two or more levels is a fall (H3). The charger takes 1d3 to its Legs, ignoring Armor, and +1 Heat.

    • F11.4 Knockdown. A melee hit that is Full or Crit from a heavier chassis class knocks the target Prone.

    • F11.5 Grapple (Full, adjacent). A Piloting contest: each side rolls d20 + Piloting + class bonus (Light 0, Medium 1, Heavy 2); the acting mech wins ties. Success: both mechs are Grappled and may not move or Boost. While grappled, either may spend a Quick to Throw (another contest; success drops the other Prone in an adjacent free hex and ends the grapple) or a Full to Break (contest; success ends it). A grapple also ends when either mech is destroyed or knocked Prone by anything else.

    • F11.6 Shields. An intact Shield arm gives melee attacks against you 1[−]. Brace's +1 Armor applies to melee as normal. Guard's hard cover does not (melee ignores cover).

    • F11.7 Precision. Aimed Shot works with any Shots-1 melee attack.

    • F11.8 Leaving a brawl. Moving out of adjacency with a hostile lets it take the Disengage reaction (E6). There is no movement cost.

G. Heat — Locked heat in v1, stress table (v0 values, tune by simulation)

  • G1 Heat comes from firing (weapon Heat), Barrage (+1), Charge (+1), Jump legs (+1 per activation with a climb), Pulse hits (1d3 each), Reactor breach crits, and Overcharge. Heat does not decay; it leaves through Vent, Stabilize, or a Stress roll.

  • G2 Stress. The moment Heat exceeds Reactor Cap, roll d6. Heat resets to 0 afterward in every case.

    d6 Result
    5–6 Emergency vent. Lose one Quick action in your next activation
    2–4 Exposed. Every part has Armor 0 until the end of your next activation
    1 Meltdown. Core takes 2d6 ignoring Armor, and you are Exposed

  • G3 Overcharge. Free action, once per activation: gain a third Quick action. Heat cost escalates per game: +1, then 1d3, then 1d6, then 1d6+4.

H. Map, terrain, sight — Locked large rectangular board, elevation, cover, LOS · Locked (preliminary) 32×20, terrain list, LOS method, three hold zones

  • H1 Board 32 hexes long by 20 deep. Deployment zones are the three rows at each short end (fronts 26 apart; a Medium reaches the middle in round 2). Large variant 40×24 with elevation up to 4.

  • H2 Elevation 0–3 per hex. A mech stands at its hex's level and is one level tall in every class. Eye height = level + 1.

  • H3 Terrain and movement

    Hex Cost Sight Note
    Open 1 clear
    Rubble 2 clear
    Foliage 2 soft cover Sight through three or more foliage or smoke hexes is blocked
    Smoke 1 soft cover Temporary (C6)
    Low wall — hard cover Impassable obstacle one level above its neighbors
    Building — blocks Two or more levels tall; roofs are hexes at that level
    Step up one level +1 Two or more levels in one step needs Jump legs
    Step down one level +0 Down two or more is a fall: Legs take 1d6 ignoring Armor, movement ends

  • H4 Line of sight. Draw the hex line attacker → target. Interpolate a sight height from the attacker's eye to the target's eye. Any intervening hex whose top is higher than the sight height at that hex blocks LOS. A top exactly at the sight height does not block; adjacent to the target it gives hard cover.

  • H5 Cover. Hard: target adjacent to an obstacle one level above its ground, between attacker and target → 2[−] and the Legs band hits the cover; ignored if the attacker is two or more levels above the target. Soft: target in foliage/smoke or the line passes through any → 1[−]. Only the best single cover applies. Guard (E5) grants hard cover from the shield-bearer's side.

  • H6 High ground. Attacker at least one level above the target gets 1[+].

  • H7 Zones. Three per map, each a 7-hex flower. You control a zone at the end of a round if at least one of your mechs stands in it and no enemy does. Placed at roughly ⅓, ½, ⅔ of the long axis, offset to different sides. Hold zones are the v0 objective; other objective types (capture and carry, escort, timed relays) are expected later and maps will be hand-crafted around them.

  • H8 Deployment. Roll off; the winner picks an end. Starting with the loser, alternate placing one mech in your deployment rows.

  • H9 Open. Deferred to v2: geometric partial cover, class height vs cover, multi-hex Heavies, additional objective types.

I. Match & scoring — Locked best of three, sideboard, kills plus objectives, values, tiebreak, clock (values preliminary)

  • I1 A match is best of three games. Rosters are locked when the match starts.
  • I2 Sideboard. Between games each player may swap one fielded mech for their fourth. Both decide simultaneously and secretly; revealed at deployment. The team must stay under the Team Cap.
  • I3 Destroying all three enemy mechs wins immediately. Otherwise the game ends after round 7 and the higher score wins.
  • I4 Score: 3 per enemy mech destroyed, 1 per zone controlled at the end of a round. Three zones over seven rounds is 21 points against 9 for a wipe.
  • I5 Tiebreak: higher Hull percentage remaining across the fielded team. Still tied: one sudden-death round, then Hull again.
  • I6 Clock: 45 seconds per activation plus a 3-minute bank per game. Real-time and asynchronous play are both planned; the clock applies to real-time matches.

J. Worked example — Example numbers

Round 3. Ruko's Reaver (Medium, Jump legs, Autocannon arm, Targeting head) jumped 4 hexes onto a level 1 rooftop. Sato's Bastion stands at level 0 five hexes away behind a low wall. Vex Locked the Bastion earlier this round. Ruko is in the front arc. Marrow is 6 hexes away (no bond bonus). Ruko's ability is active (Marrow shares Hollow Saints) and Ruko moved 3+ hexes, so the first attack gains 1[+].

Bastion Evasion = 7 − 1 (Heavy legs) + 0 (Sato Piloting) = 6. Ruko Accuracy = 2 + 0 + 1 (Targeting head) = +3. Bastion bands: Head 1, Cannon 2–4, Shield 5–8, Core 9–14, Back 15, Legs 16–20.

Step Dice Result
Modifier dice 3[+] (high ground, Locked, Ruko) vs 2[−] (hard cover) → 1[+] → d6 = 2 +2 to every shot
Shot 1 · Hit d20 = 1 Natural 1. Miss
Shot 2 · Hit d20 = 14, +3, +2 = 19 vs 6 Hit
Shot 2 · Location d20 = 18 Legs band, behind hard cover: hits the wall
Shot 3 · Hit d20 = 9, +3, +2 = 14 vs 6 Hit
Shot 3 · Location d20 = 3 Cannon arm (Armor 5, Durability 9)
Shot 3 · Penetration d6 = 4, +1 Pen = 5 vs 5 Full. Short of 9, no crit
Shot 3 · Damage 1d6 = 5 Cannon arm 9 → 4. Bastion Hull 74 → 69
Heat +2 Reaver Heat 2 of 6

This exact sequence is a unit test in engine/combat.test.ts.

K. Decision log

Locked: hex 3v3 digital, best of three with a fourth-mech sideboard · every resolution is a visible die, modifiers are dice · alternating activation with per-round initiative · heat in v1 · kills plus objectives · rectangular board larger than 20×20 with elevation, cover, LOS · Lancer stat baseline, BattleTech location and partial-cover ancestry · arms are weapons, kits are the roster unit, "roster" not "deck" · two-axis pilot synergy plus static bonds, cosmetic decoration.

Locked 2026-09-05 (were Proposed): no facing (E8) · penetration thresholds with the crit margin at Armor + 4 (F5) · crit and stress tables as v0 values (F8, G2) · scoring 3/kill, 1/zone/round, Hull tiebreak, 45s clock (I4–I6), with other objective types expected later · Fire once per activation, Barrage as the only two-weapon activation (E4/E5) · melee system (F11): Piloting for melee hits, one Strike per activation separate from Fire, Charge with push, knockdown by class, Grapple/Throw/Break now · reactions in v1 (E6): Overwatch, Backup Fire, Disengage strike, riposte.

Locked, preliminary (revisit after terrain and zones are simulated): 32×20 board, round cap 7, three 7-hex zones (H1, E1, H7). All melee and strike numbers (F11).

Open: additional objective types (H7) · roster complexity, revisit after the part catalog (B8) · v2: geometric partial cover, class height vs cover, Heavy multi-hex footprints (H9).

Placeholder numbers: every value in B and C, band defaults in F4, thresholds in F5 and F8, the stress table in G2, scoring in I4. Tune them with pnpm sim batch.

L. References