Convolute

Counter target spell unless its controller pays {4}.

Gnat Miser

Each opponent's maximum hand size is reduced by one.

Swarm of Rats's power is equal to the number of Rats you control.

Return target creature card and all other cards with the same name as that card from your graveyard to your hand.

Rat Colony gets +1/+0 for each other Rat you control.
A deck can have any number of cards named Rat Colony.