Mortuary + Woe Strider + Bolas's Citadel + Serrated Scorpion

Mortuary

Woe Strider

Bolas's Citadel

Serrated Scorpion

How it works

1. Activate Woe Strider by sacrificing Serrated Scorpion.
2. When Serrated Scorpion dies, it and Mortuary triggers.
3. Resolve the Mortuary trigger, putting Serrated Scorpion from your graveyard onto the top of your library.
4. Resolve the Serrated Scorpion trigger, causing you to gain 2 life and dealing 2 damage to each opponent.
5. Resolve the Woe Strider ability.
6. Cast Serrated Scorpion from the top of your library by paying 1 life due to Bolas's Citadel.
7. Repeat.

This loop transforms your library into a self-sustaining engine by turning Bolas's Citadel into a twisted alternate casting source that pays in life instead of mana. When you sacrifice Serrated Scorpion to Woe Strider, Mortuary intercepts the creature on its way to the graveyard and immediately places it back on top of your library. From there, Bolas's Citadel lets you cast the Scorpion right back out into play for a mere 1 life, easily offset by the life gained when Serrated Scorpion's death trigger drains your opponents.