Marchesa's Surprise Party is a rare Conspiracy — Secret Mission card from Mystery Booster 2 (MB2), collector number 503. Current market price: $0.23, TCGplayer market prices via Scryfall.
(Start the game with this conspiracy face up in the command zone. Before the game, secretly choose one of the following. During your end step, if you meet the condition, you may reveal your choice and turn this card face down. When you do, collect the reward.) • You've cast three or more spells this turn. • An opponent lost 6 or more life this turn. • There are nine or more cards in your graveyard. Reward — Draw a card.