Death-Rattle Oni

Flash
This spell costs {2} less to cast for each creature that died this turn.
When this creature enters, destroy all other creatures that were dealt damage this turn.

Shadow of Mortality

If your life total is less than your starting life total, this spell costs {X} less to cast, where X is the difference.

The Meep

Ward—Pay 3 life.
Whenever The Meep attacks, you may sacrifice another creature. If you do, creatures you control have base power and toughness X/X until end of turn, where X is the sacrificed creature's mana value.

Demon of Death's Gate

You may pay 6 life and sacrifice three black creatures rather than pay this spell's mana cost.
Flying, trample

Sibsig Muckdraggers

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
When this creature enters, return target creature card from your graveyard to your hand.

Writhing Necromass

This spell costs {1} less to cast for each creature card in your graveyard.
Deathtouch

Gorex, the Tombshell

As an additional cost to cast this spell, you may exile any number of creature cards from your graveyard. This spell costs {2} less to cast for each card exiled this way.
Deathtouch
Whenever Gorex attacks or dies, choose a card at random exiled with Gorex and put that card into its owner's hand.

Delraich

You may sacrifice three black creatures rather than pay this spell's mana cost.
Trample