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
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)
If the ninjutsu ability had been introduced in a different set, with different flavor and on different creatures, I wonder if it would have become another recurring mechanic, like cycling or convoke
These multicolor cards typically give you a good sense of what each archetypes main theme is
Retreat to Coralhelm is, therefore, a fantastic choice for the deck