Yennett, Cryptic Sovereign + Doomsday + Nexus of Fate + Necropotence

Yennett, Cryptic Sovereign

Doomsday

Nexus of Fate

Necropotence

How it works

1. Cast Doomsday by paying , searching your library and graveyard for Nexus of Fate and four other cards, then exiling the rest of your library and graveyard, putting the aforementioned cards on top of your library with Nexus of Fate being the bottom card, and causing you to lose half your life total, rounded up.
2. Activate Necropotence four times by paying 4 life, exiling the top four cards of your library.
3. Declare Yennett as attacker.
4. Yennett triggers, casting Nexus of Fate from your library without paying its mana cost.
5. Resolve Nexus of Fate, causing you to take an extra turn after this one and shuffle Nexus of Fate into your library.
6. Repeat from step 3 each turn.