What it is. The player halts, snaps downward, and hits the ground hard enough to matter — damage, a shockwave, a broken floor. The airtime before impact IS the wind-up; the impact IS the payoff.

Player fantasy / why it’s fun. You are heavy. You spend altitude and you buy consequence. It’s the one attack that reads as a decision — you left the ground, you can’t take it back, and the whole crowd below knows what’s coming.

The verb

Rise, commit, fall. The player trades mobility and horizontal control for a single concentrated hit at a point they aimed for on the way up.

How it feels / why it’s fun

• Weight. The snap-to-fall and the freeze-frame on contact sell mass. Cheap slams float; good slams drop.
• Commitment. Once you’re pounding you’ve spent your air options. That risk is the whole flavor — see pattern-risk-reward.
• The clearing. A radial shockwave that resolves a crowd in one beat is deeply satisfying. It’s the melee answer to a screen-clear bomb.

Tuning levers

Two levers carry the design: charge-by-height (the reward you earned in the air) and recovery lag (the price you pay for missing). Tune those against each other first; the rest is polish.

Slots into

• Genres: genre-precision-platformer (traversal + break-floor beats), genre-metroidvania (a gated pound that opens new floors), genre-action-adventure and genre-soulslike (a heavy, punishable finisher), genre-horde-survival and genre-bullet-hell (a crowd-clear with a cooldown baked into the recovery).
• Anchors: anchor-dead-cells (ground-slam as a committed hitbox), anchor-hades (Poseidon/heavy casts read like area slams), anchor-vampire-survivors (radial area pressure), anchor-celeste and anchor-braid as the reference for how much air-control you’re allowed to trade away.

Twist seams

• Slam but it launches you back up for a combo (structure) — impact converts downward momentum into a bounce, so a clean pound feeds a mechanic-double-jump or mechanic-combo-string instead of ending the beat. See mechanic-bounce for the momentum return.
• Ground pound but it plants a seed that grows into a platform (theme) — the slam is constructive, not destructive: each landing spawns terrain, turning an attack into level authorship. Pairs with genre-puzzle-platformer.
• Pound but the shockwave is the real attack (structure) — the fall does nothing; only the expanding ring damages, so aim becomes timing the radius, not landing on a head. Leans on system-telegraphs for both sides to read the ring.

How it wires to Hayao

• The airtime-to-impact arc is a downward velocity you clamp on the way down; the landing test is a contact against the floor collider. Read the physics parts in the platformer sandbox lab (sandboxes/ — the single-mechanic labs, not a whole game) before wiring anything.
• The shockwave is pure view — a radial cosmetic node, not part of the sim state. The hitbox that clears the crowd is simulation and must be deterministic (drive any spread/knock through the deterministic RNG, never a wall clock). Keep the ring flagged cosmetic so it stays out of the world hash.
• Freeze-frame, screen-shake, and dust are all cosmetic-side; choreograph them per pattern-juice-choreography. Do the impact-feel work against design/JUICE.md — that’s where the freeze/shake/particle timing gets proven, not here.
• For the crowd-clear hitbox, model contacts in a fixed iteration order so the same slam resolves the same enemies every run (an invariant, not a nicety).

Fails when…

• The commitment is fake. If you can steer freely mid-fall or cancel on a whim, it’s just a fast attack wearing a costume — see antipattern-false-depth. Commitment is the mechanic; don’t refund it.
• Recovery is invisible. No punish window means it’s strictly the best button and every other attack rots. That’s antipattern-boring-optimal. The lag is a feature.
• The shockwave doesn’t read. A crowd-clear the player can’t parse is antipattern-unreadable-juice — big flash, no information. Telegraph the radius and the threatened zone; readability first (pattern-readability).
• It’s the answer to everything. A pound that trivializes traversal and crowds and bosses flattens the kit into antipattern-feature-soup. Give it one job and a cost.
• The input lies. If contact damage lands before the visible impact frame, players feel robbed — antipattern-input-lie. Hitbox and impact frame fire together.

See also

• Composes with: mechanic-charge-attack (charge-by-hold vs. charge-by-height are siblings), mechanic-bounce (the launch-back seam), system-telegraphs (make the ring legible).
• Neighbors in the kit: mechanic-dash, mechanic-double-jump, mechanic-parry, mechanic-throw.
• Design context: pattern-risk-reward, pattern-juice-choreography, system-combat-model, system-encounter-design.
• Process: process-the-twist for pushing the two seams above further.