How can you play Relentless Rats in Pauper. Here's one potential Relentless Rats Pauper deck list from Mazzi di Huzen on DeckStats.
4 Barren Moor
28 Relentless Rats
4 Gray Merchant of Asphodel
Non-Creature Spells (10)
2 Death Denied
4 Geth's Verdict
4 Victim of Night
The deck is very straightforward. The Barren Moors give you the ability to cycle away itself for a single Black mana for another card if you don't need to play any more land. The 4 copies of Geth's Verdict and 4 copies of Victim of Night give you some of the best removal in Pauper. This removal is good for slowing down faster decks because each copy of Rats costs 3 mana to cast. Two copies Death Denied gives you the ability to retrieve dead Relentless Rats from your graveyard in order to continue the Rat onslaught.
Then, of course, we have 28 copies of Relentless Rats, which ensures that we always have copies of Relentless Rats to play at all times. We finish off the deck with 4 copies of Gray Merchant of Asphodel. The lynchpin in Mono-Black Devotion decks, each copy of Rats gives you 2 devotion to Black. The Gray Merchant himself gives you an additional 2 devotion. His ability drains your opponent for an amount of life equal to your devotion to Black. With just a few Rats on the board, you can end the game very quickly
Because of how long this deck can take to get going, you are going to be using your removal early and often. However, once you start getting a lot of Rats on the board, it's very difficult for your opponent to even attack you anymore. If the board becomes stalled and your army of Relentless Rats can't get through for damage, you always have the Gray Merchants to finish off the game with the drain ability. It's a pretty cool Mono-Black Devotion/Control deck.
We also found another Pauper deck list on TappedOut that uses Dark Ritual for mana acceleration, Disfigure for removal and Dusk Legion Zealot for card draw. But we prefer the Mono-Black Devotion/Control deck list better ourselves.
What do you think of Relentless Rats in Pauper? Have you ever build a Rats deck using the Relentless Rats?