You control at least one additional nontoken creature that does not have flying.
Steps
Activate
Phyrexian Altar twice by sacrificing
Slimefoot and Squee and another nontoken creature without flying, adding ({B} magic symbol) ({R} magic symbol) .
When
Slimefoot and Squee and the other creature die,
Luminous Broodmoth triggers twice.
Resolve the first trigger, returning
Slimefoot and Squee from your graveyard to the battlefield with a flying counter on it.
When
Slimefoot and Squee enters the battlefield, it triggers, creating a 1/1 Saproling creature token.
Resolve the second
Luminous Broodmoth trigger, returning the other creature from your graveyard to the battlefield with a flying counter on it.
Activate
Phyrexian Altar twice by sacrificing
Slimefoot and Squee and the other creature, adding ({1} 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 the other creature from your graveyard to the battlefield.