Activate Phyrexian Altar by sacrificing the nontoken creature, adding one mana of any color.
When the creature dies, Mortuary triggers, putting the creature from your graveyard onto the top of your library.
Cast the creature by paying its mana cost.
Repeat.
This clever loop turns the graveyard into a conveyor belt straight back to the battlefield, letting you recast the same threat over and over again. When you sacrifice a creature to Phyrexian Altar, its mana output funds the creature's re-casting, while Mortuary quietly catches it in the yard and places it right back on top of your library. From there, Eladamri, Korvecdal ensures you can see that top card and cast it directly from your library to keep the cycle spinning endlessly.