Presumed Dead is a uncommon Instant card from Murders at Karlov Manor (MKM), collector number 100. Current market price: $1.07 (foil $0.25), TCGplayer market prices via Scryfall.
Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield under its owner's control and suspect it." (A suspected creature has menace and can't block.)