You have a way to cause a creature to enter the battlefield under your control.
Steps
Cause a creature to enter the battlefield under your control, which will be legendary due to Leyline of Singularity.
Jedit triggers, causing you to pay ({G} magic symbol) to create a 2/2 Cat Warrior creature token that is legendary due to Leyline of Singularity.
The Cat Warrior enters the battlefield, triggering Jedit.
Holding priority, activate Phyrexian Altar by sacrificing the Cat Warrior, adding ({G} magic symbol) .
Resolve the Jedit trigger, causing you to pay ({G} magic symbol) to create a 2/2 Cat Warrior creature token that is legendary due to Leyline of Singularity.