The Swamp Kitten is a rare Legendary Creature — Cat card from Unknown Event (UNK), collector number RB04i.
Land creatures and/or creatures you control with menace get +1/+1. At the beginning of combat on your turn, target Swamp you control becomes a 0/0 black land creature and gains menace. It's still a land. Put a +1/+1 counter on it. (It can't be blocked except by two or more creatures. It's dark and scary.)