Alien Boss

Verified against the spelunky.ai port v0.1.10 on 27 October 2026.

The Alien Boss sits in the last room of the mothership, the alien craft some levels of the Ice Caves hold. It never moves; while the player is near, it sends a psychic wave that drifts after him and knocks him down. It has 10 hit points, and, unlike most monsters, the Whip hurts it on every step it touches it, so it doesn't last long against one. When it dies, it leaves 4 big gems and brings down the craft's barriers.

The Alien Boss doesn't move on its own: it only falls, if nothing is under it ^[3].

When the player is within 96 pixels of it, and isn't dead, stunned or invincible, it sends a psychic wave from its middle, with a sound and six sparks drawn in toward it, then waits 100 steps before it can send another, so its waves come 101 steps (about 3.4 seconds) apart at the soonest ^{[2] [4]}. It starts with that wait too, so the first wave comes 101 steps after it's made at the earliest ^[5]. The wave drifts toward the player at 2 pixels per step (60 per second), turning to follow him, until its animation ends, about 2.3 seconds later ^{[6] [7]}. It passes through walls. It hurts any other monster it touches, but not an Alien Boss, for 3 hit points ^[8]. The clip shows the Alien Boss sending a wave at the player, who loses a heart, and another about three seconds later.

The Alien Boss only acts while it's on screen or just off it ^[9].

The Alien Boss isn't stunned by hits, and the Whip and the Machete hurt it through the code most monsters share, which has no pause between hits: they take their damage on every step they touch it ^[12]. The clip shows the player whipping it: each crack took 7 hit points, and the second killed it ^[13].

Its step doesn't run the one most monsters share, so Spikes, Lava, Spear Traps and water don't affect it ^[20].

When its hit points run out, the Alien Boss dies where it is and flings out 4 big gems, each a Big Emerald, Big Sapphire or Big Ruby at random ^[21]. When its dying animation ends, every barrier emitter in the level is destroyed, and the barriers with them ^{[22] [23]}. Its body stays, and can't be picked up ^[24]. The clip shows the player dropping a Bomb beside it and running out of its range before it can send a wave; the explosion kills it. An Alien Boss killed counts toward the player's kills, and the screen between levels draws its icon ^{[25] [26]}.

Level generation makes the Alien Boss only in the mothership. An Ice Caves level after the Moai's has a 1 in 10 chance of holding the alien craft: a row of rooms from a random one to the level's right edge ^{[27] [28] [29]}. The last of them, at the edge, is the only room with the Alien Boss, beside a barrier emitter and a free Jetpack set in a block ^{[30] [31] [32]}.

In custom levels, it's the level editor's tile E ^[33].

• It only sends a wave while the player is within 96 pixels, so staying further away is safe, and walls don't stop its waves.
• A stunned or invincible player draws no wave, and a wave can't hit a stunned one.
• Its waves are 101 steps apart at the soonest: right after one is the time to get close.
• The Whip does more against it than against most monsters: two cracks are enough.

• Its step sets the same sprite whichever way it faces, in two lines ^[34].