The last level of this quest is extremely frustrating. As soon as I deliver the killing blow to the last enemy, a Festering Zombie, his festering guts ability activates and kills one of my team members, giving the enemy team the victory. I think it's unfair how the enemy team's kill is registered before mine. This is the second time I've lost this way.
I don't know your build, but: - If you have one character who can tank the zombie's attacks or has good blocks, move next to the zombie. When it's out of attacks, move another character onto a VP. - Use Barge, a weak bash (weak enough not to explode it), or a control spell to move it off the VP. - Damage it with melee attacks, then move away and finish it off with an arcane spell. Festering Guts lasts for 3 rounds (so hope it doesn't draw another). If you can tank the attacks a round or two, you can wait for it to expire before killing the beastie, but this can be a tough method. Good luck, and I hope this helps. If it doesn't, please post your race/class combos for more specific ideas. Edit: Yes, Festering Guts is unfair. But you're good enough to deal with it.
Also, Resistant Hide provides immunity to the damage from Festering Guts, so that provides a few more options for finishing it off.