You control at least one additional nontoken creature
Steps
Activate
Phyrexian Altar twice by sacrificing another nontoken creature you control and
Slimefoot and Squee, adding ({1} magic symbol) ({B} magic symbol)
When the creatures die,
Pawn of Ulamog triggers twice, creating two 0/1 Eldrazi Spawn creature tokens
Activate
Phyrexian Altar by sacrificing the two Eldrazi Spawns, adding ({R} magic symbol) ({G} magic symbol)
Activate
Slimefoot and Squee by paying ({1} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) and sacrificing a Saproling, returning it and another creature from your graveyard to the battlefield
When
Slimefoot and Squee enter the battlefield, it triggers, creating a 1/1 Saproling creature token