Dross Scorpion + Elemental Mastery + Encroaching Mycosynth + Yahenni, Undying Partisan

Dross Scorpion

Elemental Mastery

Encroaching Mycosynth

Yahenni, Undying Partisan

How it works

1. Activate the creature with Elemental Mastery attached by tapping it, creating a number of 1/1 Elemental creature tokens with haste equal to its power.
2. Activate Yahenni by sacrificing an Elemental.
3. When the Elemental dies as an artifact due to Encroaching Mycosynth, Dross Scorpion triggers, untapping the creature with Elemental Mastery attached.
4. Resolve the Yahenni ability.
5. Repeat.

This engine turns the sheer power of your board into an endless cycle of creation and sacrifice, all thanks to Encroaching Mycosynth turning every nonland permanent and token you control into an artifact. Once Elemental Mastery is enchanting a creature with sufficient power, you can tap it to flood the battlefield with hasty tokens, which Yahenni, Undying Partisan eagerly devours for sustenance. Every time one of these artifact creatures dies, Dross Scorpion wakes up to untap your enchanted creature, allowing you to repeat the ritual immediately for an unstoppable loop of sacrifices and triggers.