Contaminated Bond

Enchant creature (Target a creature as you cast this. This card enters the battlefield attached to that creature.)
Whenever enchanted creature attacks or blocks, its controller loses 3 life.

Dash Hopes

When you cast this spell, any player may pay 5 life. If a player does, counter Dash Hopes.
Counter target spell.

Liliana's Specter

Flying
When Liliana's Specter enters the battlefield, each opponent discards a card.

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters the battlefield, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Oubliette

When Oubliette enters the battlefield, target creature phases out until Oubliette leaves the battlefield. Tap that creature as it phases in this way. (Auras and Equipment phase out with it. While permanents are phased out, they're treated as though they don't exist.)

Vampiric Link

Enchant creature
Whenever enchanted creature deals damage, you gain that much life.