There are a few secret combo's that can be performed by each character. They are as follows:

Inferno --> Inferno --> Ahryu P'ung = Earthbreaker

Blizzard --> Blizzard --> Patoh Pah = Catastrophe

Quake --> Quake --> Hwajeh = Supernova

Wind attack --> Water attack --> Melee attack = Ice Sword (performed by Scias)

Fire attack --> Wind attack --> Melee attack = Phoenix (performed by Nina)

Water attack --> Earth attack --> Melee attack = Mudslide (performed by Cray)

Earth attack --> Fire attack --> Melee attack = Reflect (performed by Ursula)