Slimefoot and Squee + Phyrexian Altar + Sifter of Skulls

Slimefoot and Squee
Phyrexian Altar
Sifter of Skulls

Requires
All permanents on the battlefield. You control at least one Saproling. You control at least one additional nontoken creature.
Steps
  1. Activate Phyrexian Altar twice by sacrificing another nontoken creature you control and Slimefoot and Squee, adding 1b
  2. When the creatures die, Sifter of Skulls triggers twice, creating two 1/1 Eldrazi Scion creature tokens
  3. Activate Phyrexian Altar by sacrificing the two Eldrazi Scions, adding rg
  4. Activate Slimefoot and Squee by paying 1brg and sacrificing a Saproling, returning it and another creature from your graveyard to the battlefield
  5. When Slimefoot and Squee enter the battlefield, it triggers, creating a 1/1 Saproling creature token
  6. Repeat
Results
Infinite ETB. Infinite LTB. Infinite death triggers. Infinite sacrifice triggers.