I just lost a battle on 2-10 Hard mode, despite having a 11k power team. On the second wave, Dogface appears and after taking some damage he leaves the area, and reappears on area 3.
But Dogface is immortal on wave 2 (his HP won’t drop down from 1).
The bug is that, he didn’t leave the area of wave 2. I guess he got stunned by Cast when he was leaving, and he just stayed there fighting the whole battle. I lost the battle because I was unable to “finish in time”, but it was impossible to kill Dogface and there were no enemies left. Maybe you want to check this out, or just make him killable on the second wave.