Grolnok, the Omnivore + Timestream Navigator + Cellar Door

Grolnok, the Omnivore

Timestream Navigator

Cellar Door

How it works

1. Activate Timestream Navigator by paying 2, tapping it and putting it on the bottom of your library, causing you to take an extra turn after this one.
2. Activate Cellar Door by paying 3 and tapping it, causing you to put Timestream Navigator from the bottom of your library into your graveyard and create a 2/2 Zombie creature token.
3. Grolnok triggers, exiling Timestream Navigator with a croak counter on it.
4. Cast Timestream Navigator from exile by paying 1.
5. Repeat each turn.