There are 3 wolves, 3 kaiser wolves, and 1 Fenrir. They all have decent elemental resistances for all elements, except fire.
Fenrir is weak to strike, while the wolves are weak to slash.
The wolves often uses single target attacks that can inflict poison, and a debuffing attack, Roar, that reduces your ATK and MAG.
Fenrir often uses wide area ice attacks, and he's immune to all status ailments, except for blind.
Soon...
Espers List & Tier List (Summons)
Armors
Accessories
Great Sword
Rod (Staff)
Nagnarok
Virtuous Contract