The Tenth Doctor + Reality Strobe + Agatha of the Vile Cauldron + Mana Crypt

The Tenth Doctor

Reality Strobe

Agatha of the Vile Cauldron

Mana Crypt

How it works

1. Cast Mana Crypt by paying its mana cost.
2. Activate Mana Crypt by tapping it, adding CC.
3. Activate The Tenth Doctor by paying at most 1, removing three time counters from Reality Strobe.
4. Reality Strobe triggers, causing you to cast it from exile without paying its mana cost.
5. Resolve Reality Strobe, returning Mana Crypt from the battlefield to your hand, and then exiling Reality Strobe with three time counters on it.
6. Repeat.