Molten Echoes + Changeling Hero

Molten Echoes

Changeling Hero

How it works

1. Cast Changeling Hero by paying its mana cost.
2. When Changeling Hero enters the battlefield, its champion ability and Molten Echoes triggers.
3. Resolve the Molten Echoes trigger, creating a token copy of Changeling Hero with haste.
4. When the Changeling Hero token enters the battlefiled, its champion ability triggers, exiling the nontoken Changeling Hero until the token Changeling Hero leaves the battlefield.
5. Resolve the champion ability from step 2, exiling the token Changeling Hero.
6. The token Changeling Hero leaves the battlefield, returning the nontoken Changeling Hero from exile to the battlefield.
7. Repeat from step 2.

This clever loop hinges on the unique changeling nature of Changeling Hero, which guarantees it shares the chosen creature type for Molten Echoes no matter what type you pick. Each time the nontoken Changeling Hero enters the battlefield, Molten Echoes steps in to duplicate it, creating a hasty token copy that immediately triggers its own champion ability. By having the token exile the original and then subsequently leaving the battlefield itself (either by championing another target or through the stack's sequencing), the original returns fresh and ready to restart the cycle, generating an endless cascade of enters-the-battlefield and leaves-the-battlefield triggers.