If playing as the Silent, Piercing Wail is extremely useful, as all enemies will attack most turns. For other characters, Dark Shackles has a similar effect.
It may be best to kill the Red Slaver in the back first, so that he can't use his Entangle ability to prevent you from attacking. In addition, the Vulnerable he applies is very dangerous when 3 enemies are attacking.
After killing the Red Slaver, it may be a good idea to kill the Blue Slaver next, as it applies Weak, which will actively make your attacks less effective. However, on Ascension 18 and higher, it may be preferable to kill the Taskmaster earlier due to his Strength gain.