For every five you see, there are fifty you don't.

Rat Colony

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

Special Guests

Wreckage from the Phyrexian Invasion provided the rats with a seemingly unlimited number of breeding grounds.

Mystery Booster 2

The List

No matter how crowded the den, everyone's welcome to squeak in for the festivities.

Secret Lair Drop

Dominaria

Rat Colony's last ability lets you ignore only the "four-of" rule. It doesn't let you ignore format legality. For example, during a Bloomburrow Limited event, you can't add Rat Colonies from your personal collection.