Magic's Year of the Rat is a set of eight cards you can only get online - Polygon
Mono Black Rats for Historic - Master of Magics
A super cheap and effective way to get a win (and the 3000 XP) from 100 Card Historic Brawl : r/MagicArena
For being brave enough to play a Rat Colony deck at our PPTQ in a meta filled with Chainwhirlers and other such hate, I got a special "promo" from my LGS :