Archetype of Infestation

Archetype of Infestation gets +1/+0 for each Rat you control.
Whenever a rat dies, you may tap Archetype of Infestation. If you do, create X 1/1 black rat creature tokens, where X is Archetype of Infestation's toughness.
{t}, {b}, Sacrifice a rat: put a +1/+1 counter on Archetype of Infestation