({1} magic symbol) available, plus either ({B} magic symbol) , ({R} magic symbol) or ({G} magic symbol) available
Steps
Activate
Phyrexian Altar twice by sacrificing
Burning-Tree Emissary and
Slimefoot and Squee, adding two mana in any combination of ({B} magic symbol) , ({R} magic symbol) or ({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
Burning-Tree Emissary from your graveyard to the battlefield
When
Burning-Tree Emissary and
Slimefoot and Squee enter the battlefield, their abilities trigger