Golgari Thug + Dross Harvester + Bolas's Citadel + Yahenni, Undying Partisan

Golgari Thug

Dross Harvester

Bolas's Citadel

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Golgari Thug.
2. When Golgari Thug dies, it and Dross Harvester trigger.
3. Resolve the Golgari Thug trigger, putting it from your graveyard onto the top of your library.
4. Resolve the Dross Harvester trigger, causing you to gain 2 life.
5. Resolve the Yahenni ability.
6. Cast Golgari Thug from the top of your library by paying 2 life.
7. Repeat.