This is needed, this introduction of Skeleton Key bosses is tied to Old Scratch's promotion. Now, I know most of you will say that promotion fights aren't allowed help from friends or through team-up; but I feel an exception has to be made for this one.
1. The only way to promote Old Scratch is to defeat Nightmare Old Scratch and this is part of new side content, not main line content ( of which I count promotion of companions as being part. )
2. In most promotion quests, we're facing enemies that are level appropriate ( at or near to the companion's level ). This isn't so for this promotion, Nightmare Old Scratch is level 80 and his team are level 78.
I'm begging KI to allow team-up for the SK Old Scratch, either by ledger or at the sigil. Or reduce Nightmare Old Scratch and his team to a more managable level of level 75.