Time Sieve + Encroaching Mycosynth + Rionya, Fire Dancer + Underworld Hermit

Time Sieve

Encroaching Mycosynth

Rionya, Fire Dancer

Underworld Hermit

How it works

1. At the beginning of your combat phase, Rionya triggers, creating at least one token copy of Underworld Hermit with haste.
2. When the Underworld Hermit token enters the battlefield, it triggers, creating at least four 1/1 Squirrel creature tokens.
3. Activate Time Sieve by tapping it, sacrificing the Underworld Hermit token and the Squirrel tokens, causing you to take an extra turn after this one.
4. Repeat each turn.

This ingenious loop turns a modest devotion to black into an endless chain of extra turns, heavily enabled by Encroaching Mycosynth turning all your nonland permanents into artifacts so they can be fed to Time Sieve. At the start of your combat, Rionya, Fire Dancer creates a hasty copy of Underworld Hermit, whose entry triggers a flood of Squirrel tokens scaled to your black devotion. Because Encroaching Mycosynth makes those creatures artifacts, they—alongside the Underworld Hermit token itself—satisfy the five-artifact cost required to activate Time Sieve for another turn. You can simply repeat this process on every extra turn to lock down the game permanently.