The humps on Camerupt’s back are formed by a transformation of its bones. They sometimes blast out molten magma. This Pokémon apparently erupts often when it is enraged.
– Pokémon Alpha Sapphire Pokédex
Mega Camerupt is one of the mega Pokemon added for ORAS. It seems to be added specifically to be used by Team Magma’s boss Maxie. It even has an M on its face. It’s a counterpart to Mega Sharpedo, who is used by Team Aqua.
Stat-wise, it gains stats in every stat except Speed. In fact, it becomes slower when it mega evolves, having only 20 speed instead of 40. This makes it the slowest Fire type Pokemon (tied with Slugma, Torkoal, and Litwick).