Party mask

A party mask is someone who wears a costume or a literal mask, frequently involving a cape, and talks a lot about fighting crime. Some of them really want to be heroes, some have dreams of world domination, and some just boast about imaginary enemies they've defeated.

A party mask might have supernormal powers, or might be entirely mundane. They might think of themselves as a mask. This is a slang term for people who dress the part or talk about being a mask, but don't actually do anything. The term might also be applied to heroes who try to fight crime, but have never successfully stopped a villain.