Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Sign in Blood

Target player draws two cards and loses 2 life.

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if seven or more cards are in your graveyard.

Until end of turn, whenever a player taps a Swamp for mana, that player adds an additional {B}.

Imprint — When Chrome Mox enters, you may exile a nonartifact, nonland card from your hand.
{T}: Add one mana of any of the exiled card's colors.

Whenever you cast a spell, you gain 1 life for each spell you've cast this turn.
Pay 50 life: Aetherflux Reservoir deals 50 damage to any target.

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

Flying
{B}, Pay 2 life: Target creature gets -1/-1 until end of turn.
Whenever you lose life, draw that many cards. (Damage causes loss of life.)