Orvar, the All-Form + Venser, Shaper Savant + Submerge

Orvar, the All-Form

Venser, Shaper Savant

Submerge

How it works

1. Cast Submerge without paying its mana cost, targeting Venser.
2. Orvar triggers, creating a token copy of Venser.
3. Put either Venser into your graveyard due to the legend rule.
4. The token Venser's enter-the-battlefield ability triggers, returning Submerge to your hand.
5. Repeat.