Grave Pact

Whenever a creature you control dies, each other player sacrifices a creature of their choice.

Serra Ascendant

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
As long as you have 30 or more life, Serra Ascendant gets +5/+5 and has flying.

Bloodghast

Bloodghast can't block.
Bloodghast has haste as long as an opponent has 10 or less life.
Landfall — Whenever a land you control enters, you may return Bloodghast from your graveyard to the battlefield.

Archivist of Oghma

Flash
Whenever an opponent searches their library, you gain 1 life and draw a card.