A lot of things. Lumine is a New Generation Reploid, though unlike Axl Lumine is NOT a prototype. Lumine also contains the copy ability like Axl, though Lumine's is more "perfect" Lumine is literally able to copy a person's voice, appearance, personality, and abilities perfectly with little to no drawbacks. Lumine is capable of free flight, as well as teleportation. Lumine is sadistic, he finds pleasure in the torment of others though he is also sophisticated to some degree. He also shows some signs of insanity.
In his 2nd form Lumine is far stronger in every aspect (but he loses the ability to transform into others. Though he can still copy a person's abilities.) Lumine is also capable of a special move called "Paradise Lost" where he literally enshrouds his opponent with complete and total darkness. It is then that he proceeds to murder his opponent viciously by attacking his opponent on a mental AND physical level. (In MegaMan X8 Lumine's "Paradise Lost" is an insta-kill if not countered.) Lumine is also capable of firing and summoning energy projectiles at will in this form. The projectiles look and act like large glowing needles.
Lumine's only goal is to use Axl as a vessel to not only destroy humanity, but EVERYTHING except New Generation Reploids.
If Lumine would go against John he wouldn't need to transform into John in order to get John's abilities (and the abilities of John's suit) Lumine can copy a person's abilities near perfectly without even needing to transform into said person. Meaning he could get John's abilities and all without much of the weaknesses. Lumine would be a bit of a fair fight against others in this RP along with being a bit unfair.