Ugin's Conjurant enters and dies as a state-based action due to having 0 toughness, triggering Mortuary and Liliana, Dreadhorde General.
Resolve the Mortuary trigger, putting Ugin's Conjurant from your graveyard onto the top of your library.
Resolve the Liliana, Dreadhorde General trigger, causing you to draw a card, thus drawing Ugin's Conjurant from your library.
Repeat.
This clever loop turns the zero-cost casting of Ugin's Conjurant into a continuous engine for card draw and creature triggers. Because Ugin's Conjurant enters the battlefield with zero toughness, it immediately hits the graveyard as a state-based action, which triggers Mortuary to seamlessly recycle it right back to the top of your library. At the same time, Liliana, Dreadhorde General capitalizes on that constant cycle of demise by letting you draw a card off the top of your library each time, netting you your entire deck and limitless storm count.