Stomps that take nothing on the way up

Verified against the spelunky.ai port v0.1.11 on 28 October 2026.

A stomp takes hit points by how long the player has been falling. Most monsters' stomps take 1, and 1 more for every 16 steps of falling. A Yeti's, the Yeti King's and a Shopkeeper's take 1 for every 16 steps, rounded up, which is 0 when he hasn't been falling at all: when he stomps one while still rising.

The player jumps at a Yeti, and his feet catch its head while he is still rising: the game counts a stomp, which stuns the Yeti, but it keeps all five of its hit points ^[1].

The same rounding shows at exactly 16 steps of falling. The player hops off a ledge and lands on a Yeti on his 16th step: it loses one of its five hit points, where the same drop onto a Caveman takes two of its three ^[2].

The Yeti's stomp, which the Yeti King's and the Shopkeeper's copy, takes ceil(fallTimer/16) hit points, three times that in Spike Shoes:

else if (not other.dead and not other.stunned and (other.state == 15 or other.state == 16) and other.y < y+5 and not other.swimming)
{
    if (status < STUNNED)
    {
        other.yVel=-6-0.2*other.yVel
        if (global.hasSpikeShoes) { hp -= (3 * ceil(other.fallTimer/16)); instance_create(other.x, other.y+8, oBlood); }
        else hp -= (1 * ceil(other.fallTimer/16));
        other.fallTimer = 0;

The Yeti King's and the Shopkeeper's are the same ^{[3] [4]}. Most other monsters' stomp takes floor(fallTimer/16)+1 ^[5]. fallTimer counts the player's steps of falling, and his step sets it to 0 on every step he isn't falling ^{[6] [7]}, but a stomp needs only the player jumping (state 15) or falling (16). So a stomp while he's still rising, his middle less than 5 pixels below the Yeti's top (the Yeti King's 8), takes 0. At an exact multiple of 16 steps it takes a step's worth less than other monsters' stomps: 1, not 2, after 16 steps; at any other length the two agree ^[8].

Jump into a Yeti so that the player's feet reach its head on the way up. The replay of the first clip's staged scene, on a custom level, has the player jump as a Yeti walks up to him: he stomps it on the way up, and it's stunned with all 5 hit points ^[9]. The second's has him land on a Yeti on his 16th step of falling, which takes it from 5 hit points to 4, and the same drop onto a Caveman takes it from 3 to 1 ^[10].

The spelunky.ai port reproduces it exactly: it's in docs/quirks.md's list of the 1.1 source's bugs ^[8], and the oracle's fingerprints of both replays pin the hit points. No option turns it off.