Zer0's skill is a free kill on the toughest mob in any encounter to start it off. Hard to beat that.
Ambush+Innervate+Vel0city+Headshot+Deception = godlike base attack + godlike crit for your initial attack.
When you use a shotgun or a rocket launcher for that first attack it is devastating. If it is still alive mark it for death and then empty the rest of your magazine into it, it'll be dead unless it is some ridiculously tough badass.
Toss out a homing shock transfusion mirv grenade(these are awesome btw), find some cover, reload, wait for the grenade to strip all the shields then jump out and kill everything else.