Alien

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

No level generation makes Aliens: each comes out of a UFO in the Ice Caves that a thrown item or a thrown monster destroys, 1 time in 3. It shoots up out of the wreck, opens a parachute and drifts down, then walks back and forth on the ledge where it lands. An Alien doesn't chase or attack the player; touching it costs him 1 heart, and with 1 hit point, it dies to any hit.

When a thrown item or a stunned monster thrown at a UFO destroys it, the UFO has a 1 in 3 chance of ejecting an Alien ^{[5] [6]}. The Alien shoots straight up at 6 pixels per step, slowing by 0.5 each step and trailing flames, until it stops or meets a ceiling ^{[7] [8]}. Then it opens its parachute and drifts down at 2 pixels per step (60 per second) and 1 pixel per step to one side, which it picks at random, until a wall stops it going sideways ^{[9] [10]}. When it reaches the ground, or a web, it becomes an Alien on its feet ^{[11] [12]}; one that drifts out of the level is gone ^[13]. The clip shows an Alien parachuting from a UFO the player has destroyed, landing and walking off.

On the ground, an Alien sets off walking in a random direction at 1 pixel per step (30 per second), and turns around at walls and at the edges of its ledge, so it never walks off one ^{[14] [15]}. On a ledge with a wall or a drop on both sides of it, it stands still, facing away from the wall ^[16]. It stops to stand for 20–50 steps (0.67–1.67 seconds) with a 1 in 100 chance each step, then sets off again in a random direction ^{[17] [18]}.

An Alien only acts while it's on screen or just off it, its parachute a little further below the screen ^{[19] [20]}.

When the player touches an Alien without landing on it, he loses 1 heart, is knocked away from it, and blinks, invincible, for 30 steps (1 second), as with most monsters ^[21]. An Alien still under its parachute does the same ^[22].

An Alien on its feet has 1 hit point, so any of these kills it, leaving no body ^[23]:

The clip shows the player landing on an Alien and killing it. Under its parachute, an Alien isn't one of the monsters weapons, items and explosions hit: only landing on it kills it, and that counts as killing an Alien ^[34]. Aliens killed count toward the player's kills, and the screen between levels draws an Alien icon for each ^{[35] [36]}. One that Spikes, Lava or a Spear Trap killed doesn't count ^{[37] [38] [39]}.

Aliens appear only out of UFOs, and level generation makes UFOs only in the Ice Caves ^{[5] [40]}. A UFO destroyed any way but by a thrown item or monster ejects none ^[41].

In custom levels, it's the level editor's tile a ^[42].

• An Alien never steps off its ledge, so one on a platform stays on it.
• Under its parachute an Alien can only be stomped, so it's safer to wait until it lands than to whip at it.
• A UFO brought down by the Whip, a stomp, a bullet or a Bomb never releases an Alien.

• The parachuting Alien has a state for deploying its parachute that's never used: it goes from shooting up straight to drifting down ^{[43] [44]}.

• Its touch event starts with a comment copied from the code most monsters share, though it isn't one of them:

  // jumped on - oCaveman, oManTrap replaces this script with its own