Mothership

Verified against the spelunky.ai port v0.1.10 on 28 October 2026.

The mothership lies across a row of rooms, from one of the level's first three columns to its right edge: a hull of grey metal plates over a metal floor, closed all round. In its last room, at the level's edge, sits the Alien Boss, behind a crackling pink barrier, with a free Jetpack beside it. The level starts with the message "THERE'S A PSYCHIC PRESENCE HERE!" The code calls it the alien craft ^[3].

On an Ice Caves level after the Moai's, the mothership comes one time in 10 ^{[2] [4]}. Its roll is the other branch of the Moai's, which every Ice Caves level takes until the Moai is made, so a level before the Moai's, or the Moai's own, never has it, and the mothership only comes on levels 10, 11 and 12 ^[5]. A level with it can't also be a Yeti lair, whose roll is only made when this one fails ^[6]. It starts with "THERE'S A PSYCHIC PRESENCE HERE!" ^{[7] [8]}.

In the clip, the mothership's level loads with its message. The craft lies under the player's ledge, and the Alien Boss, in its last room, sends a psychic wave up through the hull, which knocks the player down and takes a heart ^[9].

Once the level's path is laid, the craft takes a row of rooms, the second or third, chosen at random, from a random room that isn't the last in the row to the right edge, whatever the path had put there. So it's two, three or four rooms long ^[10]:

The hull and the floor are blocks, which a bomb breaks as it does the rock, into dark rubble ^{[14] [15] [16]}. Seven of the last room's ten floor blocks are each, one time in 2, a block of the area's rock or ice instead ^[17]. The windows and the machinery inside are drawn behind, and stop nothing ^[18].

The Alien Boss doesn't move on its own, and sends psychic waves after a player who comes near, which pass through walls (its page has how it fights). When it dies, the barrier comes down ^[20].

Level generation goes over the craft's blocks as over the rock, so the Ice Caves' Yetis can stand on its floor and its hull, and UFOs hover over it ^[21].

• The barrier. The emitter in the last room's hull makes one barrier, a beam three blocks tall down to the floor, between the front of the room and the Alien Boss ^{[22] [23]}. A player who touches it loses a heart, and is thrown back away from it and made invincible for 30 steps (1 second) ^[24]. Items that touch it are thrown back to the left, and out of the player's hands; a Bomb is lit, set to go off in 4 to 8 steps ^[25]. Bullets and the Web Cannon's webs stop at it ^{[26] [27]}.
• Bringing the barrier down. Destroying the emitter destroys the barrier ^[28]. An explosion destroys it, as do a bullet and an item that hits it moving faster than 2 pixels a step ^{[29] [30] [31]}. It also breaks once it's on screen with the block above it gone, and when the Alien Boss dies ^{[32] [20]}.
• The Ice Caves' own: the drop below the level, ice, and Spring Traps (the Ice Caves' hazards).

The Jetpack in the last room is free: it's made with no price and not for sale, set in a block of rock behind the Alien Boss ^[33]. The Alien Boss leaves 4 big gems when it dies, each a Big Emerald, a Big Sapphire or a Big Ruby ^[34].

The rest of the level is as any Ice Caves level: its shops, its treasure, and Kali's altar and the Golden Idol's room in its side rooms. A shop only takes a room the path left empty, and the craft's rooms are its own by then, so a shop is never in the craft ^[35].

• The craft's floor is made of hull blocks given the floor's sprite. There's an object of its own for the floor, oAlienShipFloor, but nothing makes one ^{[36] [5]}.
• The Yeti lair's roll checks that the level hasn't got the alien craft, which it can't have by then: that roll is only made when the craft's has failed ^[37].