Aluren + Barrin, Tolarian Archmage + Mirror Image + Mirror Box

Aluren

Barrin, Tolarian Archmage

Mirror Image

Mirror Box

How it works

1. Cast Mirror Image by paying 0, choosing to have it enter the battlefield as a copy of Barrin.
2. When Mirror Image enters the battlefield, its first ability triggers, returning Barrin from the battlefield to your hand.
3. Cast Barrin by paying 0.
4. When Barrin enters the battlefield, its first ability triggers, returning Mirror Image from the battlefield to your hand.
5. Repeat.