Swamp

Stitcher's Supplier

When Stitcher's Supplier enters or dies, mill three cards. (Put the top three cards of your library into your graveyard.)

Entomb

Search your library for a card, put that card into your graveyard, then shuffle.

Gravecrawler

Gravecrawler can't block.
You may cast Gravecrawler from your graveyard as long as you control a Zombie.

Zellix, Sanity Flayer

Hive Mind — Whenever a player mills one or more creature cards, you create a 1/1 black Horror creature token.
{1}, {T}: Target player mills three cards.
Choose a Background (You can have a Background as a second commander.)

Skaab Ruinator

As an additional cost to cast this spell, exile three creature cards from your graveyard.
Flying
You may cast Skaab Ruinator from your graveyard.

Polluted Delta

{T}, Pay 1 life, Sacrifice Polluted Delta: Search your library for an Island or Swamp card, put it onto the battlefield, then shuffle.

Island

Otherworldly Gaze

Surveil 3. (Look at the top three cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Narcomoeba

Flying
When Narcomoeba is put into your graveyard from your library, you may put it onto the battlefield.

Hedron Crab

Landfall — Whenever a land you control enters, target player mills three cards.

Reanimate

Put target creature card from a graveyard onto the battlefield under your control. You lose life equal to its mana value.

Scourge of Nel Toth

Flying
You may cast Scourge of Nel Toth from your graveyard by paying {B}{B} and sacrificing two creatures rather than paying its mana cost.

Dread Return

Return target creature card from your graveyard to the battlefield.
Flashback—Sacrifice three creatures. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Underground Sea

Dakmor Salvage

Dakmor Salvage enters tapped.
{T}: Add {B}.
Dredge 2 (If you would draw a card, you may mill two cards instead. If you do, return this card from your graveyard to your hand.)