It's as powerful as you can imagine (literally)

To damn underrated, it’s an amazing power

Unless you're a mindless being.

Ok true

Everything what you imagine can make true , for example magical wand, space ship, powerfull robot who is listening your orders, or your waifu (if you had) for fun

Imagination manifestation is a broken ass power, It's so broken that in every fictional work they put limitations on it.

Perfect Imagination manifestation without limitations is so broken you wouldn't need another power literally, just imagine it and it will materialize, imagine any fictional item and it will materialize. Even illogical items since Imagination doesn't give a fuck about logic in the first place.