In Hellgate: Global on the Bridge level, there is a high possibility of running into what I call the dreaded dual-healers. Having one healer in the back is bad enough, because they will constantly heal whatever you are attacking at a rate much faster than you can damage them. On multiple occasions I ran into dual-healers, making the group impossible to kill at all since the healers would simply heal each other. In the screenshot above, I just finished killing off two mini-boss level necromancers in Path of Exile, both of whom spent the entire battle running away and summoning an enormous amount of skeletons to block the way, including resurrecting the skeletons I killed en mass.
Luckily, either the necromancers are programmed to not resurrect each other, or they simply didn’t have the chance to.