Time Sieve + Encroaching Mycosynth + Rionya, Fire Dancer + Lena, Selfless Champion

Time Sieve

Encroaching Mycosynth

Rionya, Fire Dancer

Lena, Selfless Champion

How it works

1. At the beginning of your combat phase, Rionya triggers, creating at least one token copy of Lena with haste.
2. Put the Lena token into your graveyard due to the legend rule.
3. The Lena token enters-the-battlefield ability triggers, creating at least five 1/1 Soldier creature tokens.
4. Activate Time Sieve by tapping it, sacrificing the Lena token and the Soldier tokens, causing you to take an extra turn after this one.
5. Repeat each turn.

This fascinating engine takes over the game by exploiting Encroaching Mycosynth's continuous static ability, which turns all your nonland permanents into artifacts so they can be fed directly into Time Sieve. Once Rionya, Fire Dancer triggers at the beginning of combat to copy Lena, Selfless Champion, the legend rule instantly sends the token copy to the graveyard, but its enters-the-battlefield ability still triggers to flood the board with 1/1 Soldier tokens. Because Encroaching Mycosynth has already made every single one of those new Soldiers into artifacts, you have more than enough fodder to pay Time Sieve's activation cost and claim infinite extra turns.