CellFactor: Psychokinetic Wars

Simply complete TUTORIAL and Challenges 1-10 in the Guardian Campaign. Really... none of these are tough, especially if this is the last one you do. Challenge 10 requires you to win 3 Assault rounds consecutively, which both of the others classes have as a challenge. You're required to get a 10 kill streak for challenge 9, but with the Guardian's brutal firepower from dual wielding, it shouldn't be tough.

That is why this was my favourite class online and overall. It's very powerful, and rips through most enemies quickly. The downside of this class is the loss of the Psi Shield ability, meaning little defense with high offense. You also cannot use the purple item power up (Mines for Black Op, stun for Bishop), though this isn't too much of a disadvantage.