Giant Flying Fox

Surface jungle, after dark, hardmode. That is the entire window. Not underground, not in daylight, and no item brings one out, so hunting it means standing on the jungle canopy at night with everything else that spawns there.

It flies the way every bat in the game flies: erratic, impossible to lead, changing direction every second. Homing weapons and anything with a wide arc handle it far better than a precise shot. Standing under a roof takes most of the fight away, since it has no answer to a ceiling.

In expert worlds a hit can leave you with Feral Bite, which keeps stacking new debuffs while it runs. On its own the bat is manageable. Catch that in the middle of a jungle night with everything else spawning and it is the pile of stacked effects that kills you, not the bat.

The fruit is a joke drop, a nod to the fable about a fox that decided the grapes it could not reach were sour. Real flying foxes are the largest bats alive, which is why the biggest bat in the game got the name.