Rat of Knowledge

Deathtouch, Skulk. When a rat enters the battlefield target creature gets a death counter. When a rat is put into the graveyard from anywhere, gain control of target creature in target players graveyard. When Rat of knowledge dies then destroy all creatures with a death counter on it.
{x}{x}{b}: Create X 1/1 rat creature tokens.
{b}, sacrifice a rat: Rats you control gain +1/+1 or Skulk.