Windy Balloon

These only exist while a windy day is running, and only in daylight, which is one of the narrower spawn windows in the early game. Nothing summons them and no boss gates them. They always generate on the upwind side of you, so standing still and letting the gale push you along produces nothing at all. Turn and walk into the wind instead. Once one exists it travels with the current, which means anything that appeared ahead of you is already drifting back your way. There are seven color variants and the color tells you nothing.

The balloon cannot hurt you. Only the slime tied underneath it can, and that slime is dangerous both while it is still hanging in the air and after it comes down. Popping is easy to the point of being accidental: a hit does it, walking too close does it, and it also bursts on its own if the wind carries it into terrain or into any liquid. That last part matters when you are chasing one across a lake, because the passenger simply drops wherever the balloon failed and you finish the job on the ground.

The balloon has no drop table of its own. Everything worth having is carried by the slime, and you can see it through the body the same way an ordinary bonus drop shows. That preview is the complete offer: a slime that spawned on a balloon never carries a normal bonus item on top of the balloon loot, so if the body holds nothing you want, let it float past. Kites and paper airplanes are the reason most people bother.

Popping balloons will never move your kill tally and will never unlock a banner, because the balloon has neither. Killing the slime credits that slime and only that slime. The Bestiary runs on a separate count though, and that one does want the pops, so if you are filling entries you have to burst balloons rather than only mopping up whatever falls out of them.

Kill the slime while the balloon is still whole and the string goes slack. The balloon then shoots straight upward at speed and leaves the screen. Chase it and it keeps climbing through Space until you run out of world. It also belongs to a very short list of things the game files call enemies while giving them no way to hurt anybody.