[IXRollOutIX]

I'm gonna offer some slight tweaks:

T-Rex: Strength. But maybe a focus on kicking and leg strength. The special attack could be a low powered Rider Kick. (as opposed to the form finisher being a combined four dino flame barrage kick.)
Velociraptor: Super speed, with the addition of claw weapons. The special attack can be a fury swipes quick and deadly slash sort of thing.
Spinosaurus: Adds a blade weapon. The special attack could be just a typical badass sword power-up finisher.
Carnotaurus: I'm warming up to the idea of a primarily focused fire mode, just so that it gives him a bit of ranged capability. But only if the other forms have a similar "pure" elemental mode. Maybe in this mode he focuses on punches and things as opposed to Tyrannos kicks. The special attack could be a big 'ol fire punch. I only choose Carnotarus over Allosaurus because of the more prominent horns and shorter snout. Not only does it just set it apart from Tyrannosaurus even more, but it just looks more heavy metal. Demonic maybe. Adding to the fire based theme of the mode.