Time Sieve + Mycosynth Lattice + Helm of the Host + Lena, Selfless Champion

Time Sieve

Mycosynth Lattice

Helm of the Host

Lena, Selfless Champion

How it works

1. At the beginning of your combat phase, Helm of the Host triggers, creating a nonlegendary token copy of Lena with haste.
2. The Lena token enters the battlefield, creating a number of 1/1 Soldier creature tokens equal to the number of nontoken creatures you control.
3. Activate Time Sieve by tapping it and sacrificing five creature tokens, causing you to take an extra turn after this one.
4. Repeat each turn.