Slimefoot and Squee + Phyrexian Altar + Burning-Tree Emissary

Slimefoot and Squee
Phyrexian Altar
Burning-Tree Emissary

Requires
All permanents on the battlefield. You control at least one Saproling. 1 available, plus either b, r or g available.
Steps
  1. Activate Phyrexian Altar twice by sacrificing Burning-Tree Emissary and Slimefoot and Squee, adding two mana in any combination of b, r or g
  2. Activate Slimefoot and Squee by paying 1brg and sacrificing a Saproling, returning it and Burning-Tree Emissary from your graveyard to the battlefield
  3. When Burning-Tree Emissary and Slimefoot and Squee enter the battlefield, their abilities trigger
  4. Resolve the Burning-Tree Emissary trigger, adding rg
  5. Resolve the Slimefoot and Squee trigger, creating a 1/1 Saproling creature token
  6. Repeat
Results
Infinite ETB. Infinite LTB. Infinite death triggers. Infinite sacrifice triggers.