Final Challenge, early game avoid mike, the DE owns you, but he switches to lower ranged weapons, so kill him then.

Late Game, avoid justin at ALL costs, because he tends to one shot you unless you are lucky.

I used a sniper to beat it on insane, because the super long range allows you to sometimes kill justin, and with wall hack you can pwn both of them.

(Why must you suggest that challenge Jacen? Why?)
When I originally suggested it, it utilized the zombie virus and you could cure you teammates, but hey, now you have a loyal soldier and extra health, use a sniper.

Here is my original post in the challenge suggestion thread.
Name: Infection
Mode: Modified CTF (if possible) or Deathmatch
Desc: Globex has infected some of your troops with some virus, it is spreading, and soon it will take over your team. The enemies are normal enemies, just like the infected from the first game. Every so often, one of your teammates will become infected and join their side, but you can cure them.

~~~Darth Caedus