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.

The trigger fires whenever its condition is met, but 5e RAW caps you at one bonus action per turn — so even with multiple kills, you only convert one trigger into an actual extra attack. The engine's raw postfix enforces that cap. Without raw, the cascade refires on every kill (and on bonus-attack kills): that's the cleave-style model, which matches D&D's "Cleaving Through Creatures" optional rule, ARPG cleave abilities (D4, PoE 2), and house-ruled GWM, but is more permissive than strict RAW. Mathematically both shapes are a Markov chain over (current_target_HP, attacks_remaining_this_round, bonus_pending, bonus_used) — bounded, computable, and non-trivial.

The math: PAM L5 baseline vs cascade (RAW vs cleave)

Same attack profile (Glaive, +9 to-hit, no GWM, vs AC 15). No-cascade baseline mean: 16.30 DPR.

Observations:

• RAW and cleave converge on tough queues. When the queue is short or the minions are heavy enough that the cleave model would only fire one bonus anyway ([20, 20] mostly fits — 2 mains + 1 follow-up exhausts the queue), the two numbers are within 0.5 DPR of each other.
• RAW is the more conservative model — but still ~25–47% lift on chip-minion queues. Even with the bonus-action-per-turn cap, the kill-trigger half of GWM is far from rounding error against trash.
• Cleave diverges hard against soft queues. Five 5-HP minions × 100%-kill follow-ups gives the cascade 5+ shots in a turn under cleave; RAW caps at 3. The cleave model is accurate for D4 cleave / PoE 2 chain abilities / "Cleaving Through Creatures" / house rules; it overstates 5e RAW for the GWM feat itself.

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. Under cleave, DPR is roughly identical across [12,12,12,12] and [8,8,8,8] — the bottleneck is hit-rate, not damage-vs-HP.
• Trash-fight contribution still meaningful under RAW. Baseline GWM lifts DPR from 16.30 to 21.05 (+4.75 from the trade). RAW cascade against [12,12,12,12] lifts further to 28.94 (+7.89, the kill-trigger contribution under the bonus-action cap). Cleave lifts to 36.84 (+15.79) — house rule / cleave-style territory.

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. Under RAW the bonus-action cap stops compounding past one extra attack, but reckless still makes that one extra attack reliable. Under cleave the chain depth is unbounded and the DPR more than doubles against a 4-minion queue — that's the "GWM Barb is the optimal trash clearer" math at the cleave-style end. RAW is more modest but still very strong.

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 +5.93 DPR (+36%) under strict 5e RAW for PAM L5 vs [12, 12, 12, 12] — that's ~37× larger than the +0.16 figure the boss-fight analysis surfaces. Cleave- style refire reaches +10.33 DPR (+63%), about 65× the boss number.

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.

Scope

This pillar is the per-round GWM-on-kill answer against a fixed minion queue, with RAW overkill (a 25-damage hit on a 4-HP target deals 4; the rest is wasted — engine handles this exactly). Three adjacent questions live in their own machinery:

• Cleave-style overkill carryover — the 5e Cleaving Through Creatures optional rule and ARPG cleave abilities. Different mechanic from the RAW bonus-action-on-kill model this pillar covers; pair the DPR analysis with whatever cleave rule your table uses on top of the cascade output.
• PAM reaction attacks — the polearm opportunity attack on enemies entering reach is encounter-level (positions, AI, movement). Add + <reaction_count> · E[reaction_attack] per round for whatever rate your encounter generates; the engine returns the per-attack DPR number so the composition is a single multiplication.
• Multi-encounter wave dynamics — between-fight rest, slot recovery, action-surge availability — live in the Markov rounds-to-kill machinery. The cascade gives you the per-round damage distribution; rounds-to-kill takes that distribution and runs the gambler's-ruin walk against the boss HP pool.

Build your own queue

The grammar:

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

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. Append raw to enforce the 5e bonus-action-per-turn cap; omit it for cleave-style refire on every kill.

• 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.

Where this matters in practice

"Bonus action on kill" mechanics live in plenty of systems. The cascade math here transfers directly:

Polearm Master + GWM the canonical 5e DPR build. The PAM bonus-action haft attack is a cascade target on its own — and a kill on the haft swing triggers the GWM bonus, which triggers another haft swing. The GWM break-even pillar measures the boss-fight half of this; the kill-trigger cascade is what makes PAM-GWM the strongest minion-clearing build in 5e.

Half-Orc Barbarian Brutal Critical. Brutal + reckless attack stacks crit damage and crit rate, both of which make the cascade fire more often (kills come faster, crits trigger the bonus too). The interaction with the crit-chance pillar compounds: high-crit builds get more cascade triggers against any HP queue.

ARPG cleave abilities. Diablo 4 and Path of Exile 2 cleave / chain hits are the same shape — kill triggers another swing on the next minion. The threshold question (when does cleave outpace single-target?) is the same crossover as the expected strikes result: linear in queue length once the per-swing mean covers typical minion HP.