[YuuHikari]

well... maybe we could give the final form some sort of evil drawback..like having the user turn berserk or evil or have it slowly kill him as he uses it.

The final could be based on another more powerful dino, (could be a fictional one) Not another set of dinos, just one heavily plot related one which gives him some sort of gamebreaking ability that none of the other forms could do like summon actual dinosaurs (bringing fossils to life) or summon and control whatever we call the kaijin in this story like some sort of prehistoric beastmaster.

but yeah ...so far that's all I've got for now