Nexus 99
Overview
Nexus 99 is a NPC ally you can find during the mission Break prisoners out of the Zig from Operative Wellman (CoV, levels 15 - 20). He is one of the prisoners you must help to break free out of the Zig. He will be in a cell guarded by a Private Security Captain when you find him first, and must be freed so he can help you. Once free, he will follow you and will attack any Longbow soldier or prison guard in his aggro range. Longbow will sent at least three waves of attackers against you once you free him.
During my mission, Nexus 99 had Pet class and hit points. He used Energy Blast attacks and I never saw him activate any secondary defensive powers.
Remember that at least one of the prisoners must reach the helicopter outside, so he's one of the possible mission objectives, and must survive.
Quotes
Nexus 99 seems pretty friendly, for a villain:
Before combat, in his cell: I can use some help, Villain
Once free: Thanks. You're Villain, aren't you?
If left behind: Where'd you go, Villain?
If refound: Thanks again, buddy
At the mission exit: Fine work, Villain
Information
Nexus 99 is a scientist who developed a method of tapping into an alternate dimension power source and using it as a weapon. He's been imprisoned in the Zigursky prison on grand theft charges.
Powers
This is what I saw him use during the mission: (Please note that this is just a guess, I'm no expert in Energy attacks, and would be grateful if someone could verify these attacks)
Powers
Power Bolt Ranged, Smash/Energy, Foe Knockdown
A quick attack that rapidly hurls small bolts of energy at foes, sometimes knocking them down. Fast, but little damage.
Power Blast Ranged, Smash/Energy, Foe Knockback
A much more powerful, yet slower version of power bolt. Power Blast sends a focused beam of energy at a foe that can knock him back.
Energy Torrent (Ranged) Cone, Energy/Smash, Foe Knockback
Unleashes a cone of energy that knocks foes back.
Power Thrust Melee, Smash/Energy, Foe Knockback
A powerful thrust from Nexus 99 that does smashing and energy damage and knocks foes back.