Sprouting Thrinax + Nim Deathmantle + Phyrexian Altar

Sprouting Thrinax

Nim Deathmantle

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing Sprouting Thrinax, adding 1.
2. Sprouting Thrinax dies, triggering itself and Nim Deathmantle.
3. Resolve the Sprouting Thrinax trigger, creating three 1/1 Saproling creature tokens.
4. Activate Phyrexian Altar three times by sacrificing the Saprolings, adding 3.
5. Resolve the Nim Deathmantle trigger from step 2, causing you to pay 4 to return Sprouting Thrinax from your graveyard to the battlefield, and attach Nim Deathmantle to it.
6. Repeat.