Serum Powder is a rare Artifact card from Mystery Booster 2 (MB2), collector number 142. Current market price: $1.21, TCGplayer market prices via Scryfall.
{T}: Add {C}. Any time you could mulligan and this card is in your hand, you may exile all the cards from your hand, then draw that many cards. (You can do this in addition to taking mulligans.)