I ran a tier 11 bountiful delve in Skittering Breach with this mage. The tunnels after the second boss confrontation were problematic due to a bug.
The first attack against some of the mobs would stun it a fraction of a second after it started to move or cast. When the stun wore off it would reset to spawn point and heal to 100% health. If I tried to run past it would aggro and try to fight me from that spawn point.
Eventually multiple pulls of nearby packs through them, multiple uses of invisibility, and one character death I was able to slowly pull some of them off their spawn point without the stun plus reset.
Please fix it soon. I ended up choosing to invis past the rest rather than try to deal with the bug.