Etrian Odyssey Untold's FOEs are tough puzzle-like enemies
FOE stands for Formido Oppugnatura Exsequens. They're challenging, puzzle-like enemies that appear visibly in dungeons as easily identifiable orbs, unlike other enemies that strike in random encounters. Players who are struggling would do best to avoid them until they get stronger.
The FOEs can also crash random encounters as they move one space for every step or turn in battle. So what makes them extra tough? Each FOE has its own behavioral and movement patterns, which turns them and their environment into puzzles. For example, the basic FOE, the Furyhorn, travels back and forth in a straight line while the Boulder Boars disguise themselves as piles of rocks and are quick to strike their prey — aka you.
Atlus also made a trailer available today that shows off the series-first storyline.