Dark rubble falling through the rock

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

A block of the Ice Caves' dark rock, or of the mothership's hull, breaks into one big piece of rubble and two small ones. The small ones stop on the first block they meet. The big one stops only on a brick or a stone block, which no Ice Caves level has, so it falls straight down through the rock, ice and hull below it, drawn in front of them, until it leaves the level.

The player breaks a block of the Ice Caves' dark rock with a Mattock, over a column of ice. The two small pieces of its rubble stop on the ice, but the big one falls straight down through it, in front of it, to the floor of bricks below ^[1].

The dark rock's destroy event makes one big piece, oRubbleDark, and two small ones, oRubbleDarkSmall ^[2]. The small ones are rubble pieces, whose step destroys them on any solid ^[3]. The big one has its own step, which looks only for a brick or a stone block:

y += yVel;
yVel += yAcc;

if (collision_point(x, y, oBrick, 0, 0) or
    collision_point(x, y, oBlock, 0, 0))
{
    instance_destroy();
}

The Ice Caves are made of dark rock and ice, neither a brick nor a stone block, so the piece falls on through them. It's drawn in front of them, and leaves the room through the level's open bottom, where its outside event destroys it ^[4]. Its step moves only y, so it never moves sideways: the speed a falling platform gives each of its three big pieces as it breaks is never read ^{[5] [6]}.

Break a block of the Ice Caves' rock that has rock below it, with a bomb or the Mattock, and watch the biggest piece of rubble: it falls into the rock below. The replay of the clip's staged scene, a custom level, has a block of dark rock on a column of ice over a floor of bricks. The small pieces stop at the ice, and the big one falls through all five blocks of it and is destroyed on the bricks ^[7]. In play, a UFO's laser breaks the rock on level 10 with seed 9, and the big piece falls through six blocks of rock and ice and out of the room ^[8].

The spelunky.ai port reproduces it exactly: it's in docs/quirks.md's list of the 1.1 source's bugs ^[6], and the oracle's fingerprint of the replay pins the pieces' fall. No option turns it off.