Ifrit
Leviathan
Shiva
Ramuh
Garuda
Titan
Carbuncle
Fenrir
Bahamut (Coming Soon!)
Valefor (Rumor, but unknown)
Ixion (Look at Valefor)
Diablos (Coming soon!)
Kujata (Look @ Valefor)
AirSpirit
BoltSpirit
WaterSpirit
FireSpirit
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I'll update when more info becomes available