Gaston, Despicable Dealer is a potential replacement for Doc that can get you to your seven-cost characters sooner, but because it is not inkable it may be more difficult to fit it in
Have you ever said to yourself that you want them combined into one tight Aura that busts up the game

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

Life goal maybe
The Pokmon Trading Card Game has received a new Pokmon Go expansion based on the immensely popular mobile game
Shout out to the sacrifice spells that draw you power like Life's Legacy, a sorcery at two mana and then the instant Momentous Fall that also gains life