I've never done this and know nothing about it.

But people have mentioned it, and wondered whether it's something we could run for change, as a one-off during the holidays?

Any thoughts?

If this happens at a time I can be online, I'd gladly heal these fights Bonus heals if the summoned boss is the Hitodama Confluence, which is the one I am still missing for the achievement.

The summoning ritual requires 5 people, among whom only 1 needs the fragment for the boss to summon. After these 5 people enter the portal, others (up to 40 people total I believe, the same crowd as for a Jack or Hel fight) can join; and everyone can loot from the chests after the fight.

MB can deal significant amounts of damage, use AoE, etc... The fights need a tank in good gear (or a healer better than me). As always, DPS need to pay attention to where their wandering feet might take them.

Guide : https://www.nine-swords.com/knowledge-b ... rld-bosses

So, ideally we'd need some heavy hitters in that group of five?

Nope, just a competent tank and healer - certainly helps when you have some 25-30k+ DPSers in the overall 40 people instance .. then the fight goes faster