Staff of the Death Magus

Whenever you cast a black spell or a Swamp you control enters, you gain 1 life.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Swamp

Sol Ring

Deadly Rollick

If you control a commander, you may cast this spell without paying its mana cost.
Exile target creature.

Nirkana Revenant

Whenever you tap a Swamp for mana, add an additional {B}.
{B}: This creature gets +1/+1 until end of turn.

Koh, the Face Stealer

When Koh enters, exile up to one other target creature.
Whenever another nontoken creature dies, you may exile it.
Pay 1 life: Choose a creature card exiled with Koh.
Koh has all activated and triggered abilities of the last chosen card.

Crypt Ghast

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever you tap a Swamp for mana, add an additional {B}.