Infested Thrinax enters the battlefield, it triggers, causing you to create a number of 1/1 Saproling creature tokens when a nontoken creature you control dies.
Activate
Phyrexian Altar by sacrificing
Infested Thrinax, adding ({B} magic symbol) .
When
Infested Thrinax dies, it triggers for each time it entered the battlefield this turn, creating a number of 1/1 Saproling creature tokens equal to its power for each trigger.
Activate
Phyrexian Altar by sacrificing a Saproling, adding ({B} magic symbol) .
Repeat step 5 until you either control no Saprolings, or until you have ({5} magic symbol) ({B} magic symbol) ({B} magic symbol) available, whichever comes first.