When Bile Urchin dies, Mortuary and Funeral Room trigger.
Resolve the Mortuary trigger, putting Bile Urchin from your graveyard onto the top of your library.
Resolve the Funeral Room trigger, causing you to gain 1 life and each opponent to lose 1 life.
Resolve the Bile Urchin ability.
Cast Bile Urchin from the top of your library by paying 1 life.
Repeat.
This loop relies on Gwenom, Remorseless to turn the top of your library into an alternative hand, letting you recast creatures by paying life equal to their mana value rather than their mana cost. By sacrificing Bile Urchin to drain your opponents, you trigger both Mortuary—which neatly places the urchin right back on top of your library—and the life-draining triggers of Funeral Room // Awakening Hall. This continuous recycling allows you to recast the Bile Urchin over and over, turning your life total into a lethal weapon while generating infinite death and sacrifice triggers.