Side Quest is a uncommon Sorcery card from Unstable (UST), collector number 23. Current market price: $0.13 (foil $0.50), TCGplayer market prices via Scryfall.
Target player in an Un-game you can see from your seat gains control of target creature you control until your next turn. At the beginning of your next upkeep, put two +1/+1 counters on that creature. (A creature is on the battlefield of only the game its controller is playing.)