The Tavern

Okay so if a monster's wings are bones without skin or feathers or such, how do they fly?

On gentle wafts of flavor

A wizard did it.

necromancer, but okay

I think it is a heritage from d&d. There you have different kinds of abilities, like supernatural ability, spelllike ability, extraordinary abilities, natural abilities... an undead retains only the natural abilities and loses all the other ones. So flight (bat) and losing heads (hydra) would be natural abilities and be kept, while head regrowth is a special or supernatural ability and cannot be used by hydra undead.

This at least is what I remember, it's been years.

very carefully

Well ysee they're way lighter on account of losing all their flesh and brains and, idk, whatever is in your stomach and stuff, so the bones are strong enough to keep themselves up.