The combo involves this:
Our "A" plan involves no Tortured Existence on the battlefield, our "B" plan does.
1a. Flip Infernal Caretaker to retrieve all zombies to our hand.
2a. Discard all zombies to Skirge Familiar minus 2, Carrion Feeder and Gravedigger.
3a. With 12 Black Mana, spend 1 to cast Carrion Feeder, than immediately sac Caretaker to the feeder.
4a. Spend 4 on Gravedigger, retrieving Caretaker; than sac Gravedigger to Carrion Feeder.
5a. With our last 7, Morph + Flip Infernal Caretaker, retrieving all zombies yet again.
6a. Repeat from 2a to present, except we get to pocket one mana due to not having to replay Carrion Feeder. This creates infinite mana. From here, either cycle Gempalm Polluter over and over, using the same Caretaker + Gravedigger loop, or in the combo, use Gnawing Zombie instead of Carrion Feeder for drain.
In the gempalm kill, we can always sub-out a library draw for a Dredge 5 from Stinkweed Imp, and discard stinkweed to Putrid Imp to ensure not to deck ourselves.
For our plan "B", we are assuming that we have 11 zombies in our yard, with Tortured Existence in play (P.S., Carrion Feeder is still required, while Gravedigger is not!).
1b. Flip up Infernal Caretaker, retrieving all zombies.
2b. Cast Carrion Feeder with one zombie and nom on Caretaker.
3b. Discard 8 zombos to get 8 black mana, spend 1 to swap a dud creature to swap with Caretaker and play + flip Caretaker.
4b. Rinse + repeat to get infinite mana, pocketing 1 black each time due to not having to replay Feeder.
5b. From here, either cycle Gempalm Polluter over and over, using the same Caretaker + Tortured Existence loop, or in the combo, use Gnawing Zombie instead of Carrion Feeder for drain.
