Never mulligan, and always choose to draw. Then discard a dredger to hand size.
You can discard a Phantasmagorian instead of a dredger, and then use it to discard 3 to 6 cards (you discard 6 by responding to its activation with a second activation.) Don't discard baubles.
Dredge like your life depends on it. Cast and sac baubles to hurry things along. (Gitaxian Probe would be so much better but unfortunately it's banned.)
Using your creatures to convoke (particularly the zombies you get from the four Bridge from Belows in your graveyard), cast Hogaak, Arisen Necropolis from your graveyard as often as you can. There are two of them and they're legendary, so tap one to convoke the other and keep the untapped one. You'll still need to delve 2+ cards from your graveyard for this. Keep all the finishers but delve away the rest. You should amass a stupid amount of zombies this way.
Flashback the second Dread Return on a Chancellor of the Forge, saccing nontoken creatures when possible. You get more zombies and a stupid amount of goblins.
Repeat the Hogaak cycle, tapping goblins, the other Hogaak, and zombies until you run out.
Repeat the Dread Return a Chancellor cycle twice more.
1
4 Golgari Grave-Troll
4 Golgari Thug
4 Shambling Shell
4 Stinkweed Imp
Helpers
4 Balustrade Spy
4 Ichorid
4 Mishra's Bauble
4 Narcomoeba
2 Nether Shadow
4 Phantasmagorian
4 Street Wraith
4 Urza's Bauble
4 Bridge from Below
4 Chancellor of the Forge
4 Dread Return
2 Hogaak, Arisen Necropolis
1
Gahiji, Honored One is also perfect for those colors and that theme.