Assimilate Essence is a common Instant card from March of the Machine (MOM), collector number 47. Current market price: $0.27 (foil $0.25), TCGplayer market prices via Scryfall.
Counter target creature or battle spell unless its controller pays {4}. If they do, you incubate 2. (Create an Incubator token with two +1/+1 counters on it and "{2}: Transform this token." It transforms into a 0/0 Phyrexian artifact creature.)