First Appearance: Sentinels of the Multiverse: Rook City
Who he is: The rat man of Rook City’s sewers.
Initial Side: Plaguebearer
Innate Power (Initial Side): Whenever a card named infection is destroyed, Plague Rat deals each hero target (H) (H = number of heroes) toxic damage. At the end of the villain turn, Plague Rat deals each hero target 1 irreducible melee damage.
Advanced Power (Initial Side): Increase damage dealt by Plague Rat and by infected heroes by 1.
Villain Cards that Begin Game in Play: Plague Locus (13 HP): Increase damage dealt by Plague Rat and all infected heroes by 1. At the end of the villain turn, Plague Rat regains X HP, where X = the number of infected heroes.

 
How he flips to his other side: All active heroes are infected.
Nemesis: Chrono-Ranger
Second Side: Filthy Vermin

Innate Power (Second Side): At the start of the villain turn, Plague Rat deals each infected hero 2 toxic damage. He also gives infected heroes a couple of powers as well. At the end of the villain turn, Plague Rat deals each hero target 1 irreducible melee damage.
Advanced Power (Second Side): At the start of the villain turn, Plague Rat regains (H) times 2 HP.

Most Fiendish Ongoing Card: Infection: When this card is played, if all active heroes are infected, discard this card and play the top card of the villain deck. Play this card next to an active hero who is not infected. That hero is infected. At the start of that hero’s turn, they deal themselves 1 irreducible toxic damage.

Most Fiendish One-Shot Card: Ravage: Plague Rat deals each hero target other than the hero target with the highest HP 2 toxic damage. Search the villain deck for as many copies of the card Infection as hero targets damaged this way. Play them. Shuffle the villain deck.
Most Fiendish Villain Target Card: Plague Locus (13 HP): Increase damage dealt by Plague Rat and all infected heroes by 1. At the end of the villain turn, Plague Rat regains X HP, where X = the number of infected heroes.

How to Defeat Plague Rat: You either have to eliminate his ongoing cards (Tempest, Tachyon, and Visionary to name a few heroes who can do that), or you need to ramp up the damage and wail on him. A combination of The Mighty Ra, Tempest, Legacy, and Fanatic works well. Ra’s Embrace the Flame (deal damage equal to the number of ongoing villain cards are in play) turns unstoppable with the sheer number of ongoing cards in Plague Rat’s deck.