Proteus Staff is a rare Artifact card from Mystery Booster 2 (MB2), collector number 140. Current market price: $0.64, TCGplayer market prices via Scryfall.
{2}{U}, {T}: Put target creature on the bottom of its owner's library. That creature's controller reveals cards from the top of their library until they reveal a creature card. The player puts that card onto the battlefield and the rest on the bottom of their library in any order. Activate only as a sorcery.