Mortuary + Ashnod's Altar + Crimson Kobolds + Bolas's Citadel

Mortuary

Ashnod's Altar

Crimson Kobolds

Bolas's Citadel

How it works

1. Activate Ashnod's Altar by sacrificing Crimson Kobolds
2. When Crimson Kobolds dies, Mortuary triggers, putting Crimson Kobolds from your graveyard onto the top of your library.
3. Cast Crimson Kobolds from the top of your library by paying 0 life.
4. Repeat.

This clever loop is enabled by Bolas's Citadel, which turns the top of your library into your hand and lets you cast spells using life instead of mana. By casting Crimson Kobolds, you pay zero life due to its mana value of zero, making it completely free to play from the top of your library. When you sacrifice that creature to Ashnod's Altar, you generate two colorless mana while triggering Mortuary, which neatly places Crimson Kobolds right back on top of your library to repeat the process endlessly.