From the Press Release
There's a lot about the Etrian Odyssey series that makes it different than your average role-playing game-the cartography aspect, the first-person view, the stiff challenge, and so on-but one of its most infamous features is the FOE. Short for Formido Oppugnatura Exsequens, the FOE is a special class of enemy which appears visibly in the dungeon, unlike the rest of the random encounters. And also unlike those other random encounters, an FOE stands a high chance of ruining your day if you run into one when you first meet it. The smart move is to stay out of their way until later.
In Etrian Odyssey Untold, FOEs appear on the map as clearly identifiable orbs and have unique identities on the battlefield. They move one space for each step taken or turn elapsed in battle, so it's possible to for them to crash a random encounter battle if you're not careful. To make things even more challenging, each FOE has its own behavioral and movement patterns, turning nearby FOEs and their dungeon homes into puzzles to be solved. But enough generalizing-let's show a few specifics.
Furyhorns
As the first FOE you meet, the Furyhorn is sort of a "training wheels" encounter. It moves back and forth on a preset line and won't chase you down if you stray into its line of sight. If you're feeling daring and sure that you're in no danger of getting bogged down in a random encounter-the enemy indicator gauge to the lower right helps a lot with this-then you can follow behind it to get where you need to be.
Giant Moas
These flightless birds require a bit more care on the player's part, especially when combined with partners or the hazardous terrain. They generally stay still and spend a couple of moves facing a particular direction before turning right. So long as you stay out of their field of view, they're harmless, but if they ever manage to catch sight of you, they'll give chase. If that happens, you'll have to retreat out of its territory entirely and wait for it to return to its perch before trying again. You'll definitely want to make sure your map is accurately drawn before making a second attempt.
Boulder Boars
These ugly customers "hide" in plain sight as piles of rocks and only come alive when they think they have a shot at catching their prey-namely, you. Once they shed their disguise and rear up, your next move had better be to get out of their way; if it's not, you'll find your party smack in the path of their lightning-quick rampage straight forward. This is easily done when you're only dealing with one at a time, but if you ever find yourself in a whole room dotted with the things, you'd best step lively to avoid being gored.
Jungle Killers
These FOEs have the particularly nasty habit of breaking the rules and not showing up on the field until you're only a couple spaces away, at which point they break from cover and begin chasing you down. If you find yourself suddenly faced with one, your only option is to try to use the environment to get around its hiding place so you can get past. If you haven't yet mapped out enough of the surrounding area, you can also try retracing your steps far enough that it loses interest.
Reaping Shades
You'll meet these terrors in wide, open spaces, and you'll need the room. They home in on you from the instant you enter their territory and never let up until you find your way out. To get past them, you'll need to perform a sort of grim waltz: they'll only take two steps for every three of yours, which can give you the slight opening you need to get past. Just be careful not to squander that opportunity in a random battle as you try to gain that slight lead, or they could be breathing even closer down your neck.
To learn more, visit the official Etrian Odyssey Untold website.