[Dundee Slaytern]

I haven't got the chance to try this on HoF-mode yet, but some suggestions that might help.

If your Wizard is capable of doing so, continuously cast Disintegrate on their Wizard, Summoner, and Archer in that order respectively.

Stubby will chase after his target come hail or fire, with nothing to distract him. Observe which party position will teleport to the location nearest to him, and place your least needed party member there for him to lock on as a target. The sole purpose of this party member is to run around like a mad chicken throughout the WHOLE FIGHT (make judicious use of the Pause function). A Hasted Bard with Boots of Speed may be your best bet here.

Choppy can be easily distracted with summons.

Monky is the hardest to rein in as he is willing to change targets if need be. Get your best tank to distract him, and don't hesitate to swap tanks when necessary.

Pre-cast Insect Plague/Creeping Doom at where the Wizard and the Summoner will be. If you can stop their spellcasting, they're harmless. Alternatives include multiple Webs with a Sword Spider or two.

Also... don't forget that they're Undead. If you have any Weapons of Disruption, now is the time to bring them out. Be it Arrows, Bullets, Maces, etc...

Cheers.