Aliens? Probably. We know planets are common and there’s nothing to suggest that life could only evolve once. I’m skeptical of claims that any are actively visiting Earth, though.
Fairies, pixies, unicorns, djinn, etc.? No way. Gods at least have some ontological arguments in their favor: for example, is it more parsimonious to describe a universe that started existing out of nothing or a deity that exists outside of the universe’s constraints? Neither explanation is particularly satisfying, but at least both are considerable.
Fairies, however, don’t add anything to the discussion and can therefore be dismissed out of hand.