Eel, Blockade: A relative of the Luray Eel, this subterranean predator lacks it's relative's concealment tallent, but can expand to completely fill the tunnel in which it hunts.
Eel, Giant: If your sea serpent problem isn't a wyrm, it's one of these. Tenacious, mean, and just as likely to constrict your vessel into kindling as it is to snatch people off the deck with a mouth full of pointy teeth. Giant eels are not amphibious, and can only breathe water.
Egg-baiter: a sort of snail whose shell grows in the shape of an egg. Their preferred food is actual eggs, and they will move into a nest, and over the course of a few days drill into all the real eggs to consume the contents. They are also venomous, capable of injecting a neurotoxin into creatures several times their size, disabling them, and allowing the Egg-baiter to consume them as well. Chocobo egg sized ones have been reported, though to date, none the size of wyvern or drake eggs have been sighted.
Elemental, Wild: During times of appropriately extreme environmental conditions, an elemental spirit will physically manifest and wander about, investigating the physical realm with the curiosity of your average bear cub. While this does make binding them to your service much simpler, it also allows them to lash out with elemental magics at whatever annoys them with impunity.
Executrix: At rest, this creature resembles a 6' tall drake egg. When provoked, it will stand up on it's four 12' long bird legs, and lay into its antagonists with powerful kicks and rending strikes. Apparently the mouth is on the bottom, for after the fight, it will settle down on top of its prey to feed. The shells are valuable intact, and serve as an excellent cook-pot once you've dismembered the beast.
Eye, Floating: A lidded eyeball with bat wings on either side. They come in a variety of sizes, ranging from grapefruit to beach ball, and gain more and stronger gaze powers the bigger they get. While they can be bound as familiars, they generally go about deliberately making people's lives more difficult, frequently by abetting the activities of larger monsters.
Eye Tyrant: A floating eye that has lived long enough to grow a mouth and develop language skills. For an unknown reason, they have an affinity for Demonology magic, and gleefully summon in entities Best Left Alone.