Day of the Dragons + Starfield of Nyx

Day of the Dragons

Starfield of Nyx

How it works

1. Cast Day of the Dragons by paying 4.
2. Day of the Dragons enters the battlefield, triggering itself, exiling itself and all other creatures you control and creating a 5/5 Dragon creature token for each creature exiled.
3. When Day of the Dragons leaves the battlefield, it triggers itself, causing you to sacrifice all Dragons you control and return Day of the Dragons and the other exiled cards to the battlefield.
4. Repeat from step 2.
5. Note that this is a mandatory loop that will end the game in a draw unless you have a way to end it or to use it for a game-winning effect.