Phyresis Outbreak gives poison and might kill opponents creatures Feed the Swarm enchantment removal in black Vat Emergence gets a creature back and proliferates Spread the Sickness destroys a creatures and proliferates Pact of the Serpent strong tribal card draw Living Death swap graveyards with battlefields, great after sacrificing your whole board to draw cards Skullclamp sack small rats for card draw Thrumming Stone if you go the Relentless Rats or Rat Colony route Coat of Arms your rats will be huge Bolas's Citadel this card is dumb lol, lots of casting power and then you hit Gray Merchant of Asphodel and keep going lol Icon of Ancestry kinda draw buffs rats...is ok Contagion Engine proliferate twice each time you activate Eldrazi Monument gives creatures flying indestructible and +1/+1 Grafted Exoskeleton gives a creature infect, great with Crypt Rats Sword of Truth and Justice proliferate sword Bad Moon buff all black creatures, opponents too Phyresis gives infect again good with Crypt Rats Greed card draw Vraska, Betrayal's Sting proliferate planes walker I know that's a lot but hopefully gave you some ideas to work with

Latias ex gives basic Pokmon in play a free retreat cost
As the natural cycle of day and night grew twisted, old powers stirred deep in the Ulvenwald
Cards that show Pokmon interacting with each other like this really add depth to the series and often happen to be totally adorable while doing so
Atogatog Copy And Paste Atog is a popular creature (maybe less loved if you played Pauper) that spun off into a series of other Atog cards, each with the gimmick of sacrificing a permanent to give temporary stat boosts
Creature - Giant Color tag templates(None) Graveyard Marshal , Exile a creature card from your graveyard: Create a tapped 2/2 black Zombie creature token