Double-speed Olmec and boulder

Verified against the spelunky.ai port v0.1.13 on 28 October 2026.

Olmec and the boulder that the golden idol lets loose are moving blocks, which the game moves by their speed every step. Their own code then moves them by that speed again, so each covers twice the speed its code sets. Nothing on screen says so: it shows as an Olmec who flies faster than his numbers, and a boulder that rolls at 8 to 10 pixels a step where its code says 4.5.

Olmec hops toward a player standing still. He leaves the ground at 8 pixels a step, where his speed is 4, and drifts left 4 pixels a step, where his speed is never more than 2. Over the player he stops, then slams down 10 pixels a step, where his speed is 5, and crushes him ^[1].

The player has taken the idol, and the tiki head drops the boulder onto him. Its speed is 4.5 pixels a step as it rolls off, and once it's clear of him it moves 10, 8, 10 and 8 pixels a step ^[2].

Each step, the game first moves every moving block (oMovingSolid, which Olmec and the boulder are) by its speed, pushing and carrying the player ^[3]. Away from the player, that's the plain move at the end:

  else
  {
    x+=xVelInteger
    y+=yVelInteger
  }

Then each block's own step runs. Olmec's moves him by the same speed again, with moveTo, which stops at blocks:

if (carryPlayer or collision_rectangle(x-1, y, x+66, y+62, oPlayer1, 0, 0))
{
    oPlayer1.x += xVel;
    oPlayer1.y += yVel;
}
moveTo(xVel,yVel);

The boulder's does the same ^[4]. Both moves turn a fraction of a pixel into whole pixels the same way, by the step's count ^[5], so in the open the two moves are the same and each covers twice its speed ^[6]. The game's other moving blocks, such as the Ceiling Trap and the Smash Trap, either only set their speed and leave the moving to the game, or move by variables of their own, so they move once.

It happens in every Olmec fight and to every boulder the idol sets off. In the first clip's replay, Olmec hops toward the player on frame 2908: his y goes 496, 488, 480, 472 on 2909-2912, with his speed -4 and slowing; his x goes 72, 68, 64, 60 on 2925-2928, with his sideways speed never past -2; and slamming, his y goes from 416 to 426 on 2954, with his speed 5. Gaining a fifth of a pixel a step after that, his speed is turned into 5 or 6 whole pixels for each of the two moves, so he falls 10 or 12 pixels a step. The slam crushes the player on 2964 ^[7]. In the second's, the boulder's speed is 4.5 from frame 813, and its x goes 118, 128, 136, 146, 154 on 817-821 ^[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 fingerprints of the two replays pin the moves. No option turns it off.