Tidespout Tyrant + Mana Vault

Prerequisites

You control a nontoken permanent that can be cast using {C}{C}.

Steps

1. Cast Mana Vault by paying its mana cost.
2. Tidespout Tyrant triggers, returning a nontoken permanent that can be cast using {C}{C} from the battlefield to your hand.
3. Activate Mana Vault by tapping it, adding {C}{C}{C}
4. Cast the nontoken permanent returned in step 2 by paying its mana cost.
5. Tidespout Tyrant triggers, returning Mana Vault from the battlefield to your hand.
6. Repeat.