I expect Lantern of the Lost to see play across a variety of formats
Since Sothera exiles, it prevents those creatures from triggering death triggers, and lets you take a creature for yourself if a battlefield is ever empty
With Phelia, your gameplan is much deeper as you try to accrue value from your Enter the Battlefield effect abilities, and despite being a MonoColor deck you can go toe-to-toe with the Blue decks and even be able to outgrind them
In metagames rife with Reliquary Towers and full grips, this is going to be obscenely good (because it'll be like a 30/30, and it will tutor for that Strip Mine, Dust Bowl, and/or Wasteland to destroy the Towers)
Retreat to Coralhelm is, therefore, a fantastic choice for the deck