Great Weapon Master on kill — the underweighted half of the GWM math

The two halves of GWM's bonus

Per RAW: "When you score a critical hit with a melee weapon attack or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action."

Two trigger conditions, very different probabilities:

• Crit-trigger — fires on a natural 20 (or natural 19-20 with Champion). Fixed 5-10% per attack regardless of target. Against a stationary boss, contributes P(≥1 crit in chain) · E[bonus per attempt] ≈ 0.1-0.5 DPR — small.
• Kill-trigger — fires whenever an attack reduces a target to 0 HP. Probability depends on per-attack damage vs current target HP. Against a stationary boss with many HP, fires never (trigger probability ≈ 0). Against a queue of minions you can one-shot, fires reliably and chains when bonus attacks themselves kill.

Per Sage Advice (Crawford), the trigger refires on each kill — so a fighter reliably one-shotting minions can chain several bonus attacks per turn. The cascade is mathematically a Markov chain over (current_target_HP, attacks_remaining_this_round, bonus_pending) — bounded, computable, and non-trivial.

The math: PAM L5 baseline vs cascade

Same attack profile (Glaive, +9 to-hit, no GWM, vs AC 15):

Observation: against a single low-HP target the cascade actually underperforms the no-cascade baseline because the queue runs out and subsequent attacks (main + bonus) deal 0 damage — overkill waste. The cascade pays off when the queue is long enough to absorb every chained attack. Sweet spot: queue length ≈ main_count × 2-3 (so every main and chained bonus has a target).

PAM+GWM with the −5/+10 trade

Same Glaive build, GWM penalty applied to all attacks (1d10+15 @ AC15 +4):

Two notes:

• HP doesn't matter much when 1d10+15 always one-shots. With per-attack damage 16-25 (mean 20.5), a 12-HP target and an 8-HP target both die on every hit. Cascade DPR is identical across [12,12,12,12] and [8,8,8,8] — the bottleneck is hit-rate, not damage-vs-HP.
• Trash-fight contribution dominates the −5/+10 trade. At baseline, GWM lifts DPR from 16.30 to 21.05 (+4.75 from the trade). Cascade against [12,12,12,12] lifts further to 36.84 — that's another +15.79 from the kill-trigger half. The trade adds 30%; the cascade adds another 75% on top.

The Half-Orc Barb 5 extreme case

Reckless Attack (advantage to hit) doubles per-attack crit rate; Savage Attacks adds a brutal die on melee crits. Combined with GWM and a 4-minion queue:

Reckless advantage compounds: it doubles per-attack hit rate, which doubles cascade trigger rate, which extends the cascade depth, which… you get the idea. Against a 4-minion queue the cascade more than doubles the no-cascade DPR. This is the "GWM Barb is the optimal trash clearer" math made exact.

The boss-vs-trash gap

The headline number from the GWM break-even pillar was that the bonus-on-crit clause contributes only +0.16 DPR — measured against a stationary boss (full mutex 30.09 minus PAM+GWM-trade-only-no-bonus-on-crit 29.93 = 0.16).

Against minion queues the cascade contribution is +4.58 DPR (+21%) for the same PAM+GWM L5 build vs [12, 12, 12, 12] — that's 28× larger than the +0.16 figure the boss-fight analysis surfaces.

Both numbers are correct, but they answer different questions:

• "Should I take GWM if all I do is fight bosses?" — the boss-fight analysis. Answer: take it for the −5/+10 trade; the bonus-on-crit clause itself is rounding error.
• "Should I take GWM if my campaign has lots of trash?" — this pillar. Answer: take it for the kill-trigger cascade too; the bonus is far from rounding error against minion waves.

What the engine doesn't model (yet)

• Overkill carryover (Cleave-style) — the RAW melee rule has no carryover (a 25-damage hit on a 4-HP target deals 4 damage; the rest is wasted). The engine models this. Cleave-style mechanics where the overkill carries are a separate variant (5e Cleaving Through Creatures optional rule, various ARPG cleave abilities) and aren't yet wired into the cascade.
• PAM reaction attacks — the polearm opportunity attack on enemies entering reach is encounter- level (positions, AI, movement) and doesn't fold into a single DPR number cleanly. Rough approximation: add + <reaction_count> · E[reaction_attack] per round for whatever rate your encounter generates.
• Multi-encounter wave dynamics — between-fight rest, slot recovery, action-surge availability, etc. The cascade computes per-round damage against a fixed queue; longer scenarios need composition with the Markov rounds-to-kill machinery. That composition exists in the engine but isn't yet surfaced as a single expression.

Engineering scope for the open extensions lives in docs/engine-extensions-queue-and-reactions.md in the repo.

Build your own queue

The grammar:

<attack> @ AC<n> +<m> attacks N cascade [HP1, HP2, ...] onkill <attack>

Brackets and comma separators are optional in the URL form (slug encoder strips brackets, accepts _ as a separator). Each HP must be in [1, 10000], queue length 1-50, cascade depth capped at 8 per round.

• 1d10+5 @ AC15 +9 attacks 2 cascade [12, 12, 12, 12] onkill 1d10+5 @ AC15 +9 — PAM L5 vs four 12-HP minions
• 1d10+15 @ AC15 +4 attacks 2 cascade [12, 12, 12, 12] onkill 1d10+15 @ AC15 +4 — PAM+GWM L5 vs the same queue
• 1d10+17 @ AC15 +4 adv brutal1 attacks 2 cascade [12, 12, 12, 12] onkill 1d10+17 @ AC15 +4 adv brutal1 — Half-Orc Barb 5 with rage+reckless+savage vs the same queue

Full grammar at /syntax.