Someone datamined the different carbuncles way back in phase 2. There was also a ruby carbuncle, and I think it was the tank version if memory serves. It sounded like the different versions were unlocked by class quests (the same way THM gets their instant blast spell and CNJ gets their water blast at level 15).
I'm a tinker! Tinkerer? Hrm.... I'm an artificer! - Myxie Tryxle | Impressions and Memories