Cast Through Time + Venser, Shaper Savant + Erratic Portal + Nexus of Fate

Cast Through Time

Venser, Shaper Savant

Erratic Portal

Nexus of Fate

How it works

1. Cast Nexus of Fate by paying 5, granting you an extra turn after this one and exiling it due to rebound.
2. At the beginning of your next upkeep, rebound triggers, causing you to cast the exiled spell without paying its mana cost.
3. In response, activate Erratic Portal by tapping it and paying 1, returning Venser to your hand.
4. Cast Venser by paying 2.
5. When Venser enters the battlefield, they trigger, returning the extra turn spell to your hand.
6. Repeat each turn.