Riftpox, the Soul-Fester

Deathtouch, skulk
Other Rat creatures you control get +1/+1 and have deathtouch and skulk.
Whenever a creature dealt damage by a rat you control dies, create a 1/2 black rat creature token.
Whenever a rat you control deals damage to an opponent, that player puts the top card of his or her library into his or her graveyard.