Poltergeist

Artist: Andrew Bosley
Card Text	Play: Use an artifact controlled by any player as if it were yours. Destroy that artifact.
Stats	Amber:1
Type	Action
House	Dis
Rarity	Uncommon
Sets	CotA(069), AoA(080), WC(094)

FAQ

My opponent has a Banner of Battle (CoTA 020) in play. Can I play the card Poltergeist (CoTA 069) to destroy the Banner of Battle, even if the artifact can’t be used?

Yes, you can resolve the effect of Poltergeist on any artifact in play even if the artifact cannot be used. You just resolve as much of the card effect as you can and to resolve this situation you just destroy the artifact.