In Baldurs Gate II, he cant use weapons, wear armor, or use items other than potions
For this deck, though
Mirrorhall Mimic is a four-mana Blue 0/0 that enters the battlefield as a copy of any creature on the battlefield, but it'll also be a spirit in addition to its other types
It makes sure your deck is consistent and complete, helping identify what your deck might currently be lacking, letting you refine your deck lists independent of playtesting
In fact, it's likely we won't see it again, and future Universes Beyond products will use their own, similar keywords
And its among the best get out of jail cards when you're caught between a rock and a hard place: You draw a full new hand, and after you cast anything useful from it you get your old hand back