Alchemist's Gambit is a rare Sorcery card from Magic Online Promos (PRM), collector number 95375.
Cleave {4}{U}{U}{R} (You may cast this spell for its cleave cost. If you do, remove the words in square brackets.) Take an extra turn after this one. During that turn, damage can't be prevented. [At the beginning of that turn's end step, you lose the game.] Exile Alchemist's Gambit.