Kozilek's Return

Devoid (This card has no color.)
Kozilek's Return deals 2 damage to each creature.
Whenever you cast an Eldrazi creature spell with mana value 7 or greater, you may exile this card from your graveyard. If you do, this card deals 5 damage to each creature.

Pioneer Masters

Modern Horizons 3 Commander

Devoid (This card has no color.)
Kozilek's Return deals 2 damage to each creature.
Whenever you cast an Eldrazi creature spell with mana value 7 or greater, you may exile Kozilek's Return from your graveyard. If you do, Kozilek's Return deals 5 damage to each creature.

Oath of the Gatewatch

Devoid (This card has no color.)
Kozilek's Return deals 2 damage to each creature.
Whenever you cast an Eldrazi creature spell with converted mana cost 7 or greater, you may exile Kozilek's Return from your graveyard. If you do, Kozilek's Return deals 5 damage to each creature.

Oath of the Gatewatch Promos

Exiling Kozilek's Return due to the last ability isn't the same as casting it as a spell. Cards that say "Counter target spell" won't work.

The last ability triggers only if Kozilek's Return is in your graveyard as you cast the Eldrazi creature spell. That ability will resolve before the Eldrazi creature spell does. In other words, that Eldrazi won't be on the battlefield yet and won't be dealt damage by Kozilek's Return.