[@Pearion_Rehtyer] Well, by basic racial capabilities, Fava is the toughest of the three, while Dexter is clearly the one capable of dishing out the most punishment. Their movesets reflect this, and I think Fava can adopt a supportive role if he likes with the abilities he has. Thassa on the other hand is much bigger than either of them and more mobile (although probably not as fast as Dexter) - capable of getting just about anywhere, because, y'know, snake. So with moderate speed, durability, and attack (although outside of the statistic slant she'd have considerable strength due to her size), her 'role' is a little tougher to pin down. 
Maybe she's there to look scary/pretty? <3.