UFOs are dangerous flying enemies found in the Ice Caves, the Worm, or the Mothership.
When passive, UFOs generally patrol a horizontal space, only turning when they reach a wall. They have quite a large aggro range making it difficult to sneak by one without it noticing you. Once it finds a target, it will attempt to manoeuvre into a spot a few tiles directly above the Spelunker, where it attacks by firing a slow-moving plasma bolt straight down. This bolt will destroy the first block it touches if it does not hit an enemy. For this reason, you should be careful about fighting UFOs near to Altars and Shops.
Upon death, the alien pilot will attempt to eject and parachute toward the nearest safe land whilst the abandoned craft will fall to either side, exploding on any surface it touches. This can be very unpredictable, so always be prepared for the UFO to explode anywhere.
Be extra careful while killing UFOs with a boomerang, as the return flight of the boomerang can often drag the exploding ship all the way back to you. This is more common if the UFO is on the edge of the boomerang's range. Something interesting is that sometimes when you hit it it will spurt blood even if the alien ejects safely.
UFOs are a tricky enemy, in that killing them can be riskier than leaving them alive, but the reverse can also be true.
UFOs will usually attempt to fly upwards to attack you, and therefore do not usually fly downwards unless the Spelunker descends a significant distance below them. This behaviour usually leads to the UFO trapping itself in a n-shaped alcove, unable to fly sideways until the player moves downwards. The player can use this to their advantage to escape troublesome UFOs.
UFOs themselves and their plasma bolt attack move quite slowly, so it is quite easy to bait them into destroying terrain that contains treasure, as long as there are no other dangers such as Yetis or Mines around.
The UFO plasma bolt is one of the only things able to damage the Ghost, the other being lava. Given that the Ghost has 9999 health and the bolt does 1 damage to it, it isn't very useful, but it can move the Ghost out of the way.
The UFO plasma bolt can also deflect objects thrown at it, such as bombs, rocks or landmines.
The damaged, falling UFO may be caught, but is heavy , so is dropped at the end of the level and explodes.