Alright, I'm very tired and on vacation when I'm writing this, so forgive me if any of it is poorly worded or anything like that.
Name: Montresor (registered name; universally believed to be a stage name of some sort)
Age: 25
Sexual Orientation: Rumored to be bi, but no one seems to look for evidence either way when there's more interesting scandals in his fighting life.
Appearance: 
(Without the claws, obviously. Wears
this whenever he's in or around an MBF fight.)
Personality: In the ring, Montresor does everything he can to be a showman. He constantly taunts his foes and tries to draw them into taking risks that will be sure to entertain, even though he makes himself lose sometimes. He generally tries to drag every fight out as long as possible, only stopping when either he or his opponent has completely run out of energy. Occasionally, he'll back off and even hold his team (when he's on a team) back if he feels he's crippled an enemy out of sheer luck, giving them time to recover.
Outside of the ring, whatever little time he spends around the other pilots, he acts fairly polite to most, but gets violently enraged if anyone insults him or suggest that he's playing outside the rules (an accusation that will be discussed later). Twice he's hospitalized another pilot, and on one of those occasions had to get admitted himself. You don't often see him around his competitors and teammates, though; he usually collects his winnings immediately after the fight, then changes and leaves out the spectator entrance to avoid the usual post-fight interviews.
All in all, it's difficult to say how deep this nutjob persona of his goes; whether it's just an act he puts on to draw a crowd, or if he really is unhinged.
History: Very little. Montresor entered the league three years ago, funded by an anonymous sponser. His Mobilized Weapon was already fully outfitted and he was more or less fully trained. He immediately jumped into the big matches, sometimes making a guest appearances on various teams that were short one member, but generally sticking to the one-on-one and occasionally two-on-two battles. Very little has changed since that time, except for slight rises and dips in his skill based around whether he was on a winning streak or losing streak during those times.
Of course, as he got popular to be recognized by a good chunk of the population when brought up by name, the media started researching and publishing poorly-founded rumors regarding his sponsors and his erratic win-loss patterns. Soon enough, everyone believed Montresor was funded by one of the mafias, and that he was purposely winning and losing certain matches so that his bosses could make big money by placing bets on a predetermined outcome. When the Federation looked into this, they found no evidence that he was rigging or intentionally throwing any matches, so he hasn't been banned from the league just yet.
A few rumors also refer to a
violet-haired woman who is often seen around his garage when his mech is getting repaired, though no one has been able to get close enough to question her yet.
MW
Name: Terror Grand
Appearance:
Standard Weaponry-Two sets of three claws that flip out into attack position rather than extend and retract. Can be either coated with plasma or charged with electricity.
-Beam emitters on both palms that shoot small energy rings.
Optional Weaponry-Dispenser unit, on back. Can either be loaded with mines (20 max), flammable gel, or a smokescreen. Montresor usually doesn't bother, though.
Other Systems-Lock-resistant armor coating. Makes it slightly easier for him to throw off the detection system for a weapon lock by moving around.
Construction and History: Again, there is little public knowledge on the matter. Montresor simply showed up to register with the unit already on hand and has done very little to modify or upgrade it since. It may not have even been made specifically for his use, though skilled pilots may recognize that the machine does seem to fit his style quite well with its speed and oddball design.