Ugin's Conjurant enters and dies as a state-based action due to having 0 toughness, triggering Mortuary and Grim Haruspex.
Resolve the Mortuary trigger, putting Ugin's Conjurant from your graveyard onto the top of your library.
Resolve the Grim Haruspex trigger, causing you to draw a card, thus drawing Ugin's Conjurant from your library.
Repeat.
This clever loop turns the self-sacrificing nature of Ugin's Conjurant into an infinite card-drawing machine. As the zero-cost construct repeatedly enters and instantly dies from having zero toughness, Mortuary acts as the guardian of the cycle, seamlessly intercepting it from the graveyard to place it right back onto the top of your library. Meanwhile, Grim Haruspex watches the endless procession of dying creatures and cashes out each demise into a drawn card, seamlessly pulling Ugin's Conjurant back into your hand to repeat the process indefinitely.