Six-boxed this guy on Agnarr in an instance. Mostly maxed out level 65 toons, dru cle enc mag wiz bard. Druid tanked. Stuck cleric behind a wall and he avoided one of the two dots. Forget which tho lol. His guards can be split out and that's advisable. They can't be mezzed and do summon. Beyond that, kinda long fight so watch mana. Not a challenge if tank is robust and cleric can maintain mana, especially if just Complete Heal is sufficient. Chanter slow landed. Grummus is not very spell-resistant. Every dot seemed to land first shot and most nukes were unresisted.
Lockout on instance is 2.5 days. In open world Grummus and the Key holder mob respawn in 5 hours, I believe.
Grummus has about 567k hps.
Second time I fought him in an instance, clearing his guards. Was creeping my toons one by one into his "anteroom" and he aggro's on the 5th toon. Dunno why. They all moved into position the same way, Perhaps he paths close to the other side of the door and at some point gets into proximity aggro range.
Note that Grummus wanders slowly between 3 rooms, pausing for a few minutes in each room. This allows you to set up in the first room comfortably if you wait till he moves out, since he is going to go to each room, pause a bit, and then come back, pausing again in each room. Helps especially when boxing.
Edited, Dec 22nd 2023 10:01pm by Sippin