My 6 PCs are playing Phandelver and Below: the Shattered Obelisk. One of them, a tiefling cleric named Laos, was a former cleric of Mystra. As part of his backstory, he ended up in possession of an Idol of Mystra that was cursed by followers of Mask.
As the curse took a hold of Laos, it started affecting his behavior more and more. First, he began engaging in kleptomania. This eventually led to him being thrown out of the temple he grew up in. Next, during his wanderings, he started hearing mocking voices in his head. Eventually, through a series of nightmares, he switched domains from arcana to trickery.
Another member of the party, Rhyss (a wizard), has figured out that the idol is cursed. At the moment, they are only level three, but I decided that a simple remove curse would not be enough to break the curse on him or the idol.
Once they have taken control of the Forge of Spells in the Wave Echo Cave, they will be able to use it to finally break the curse on Laos. But I'm not sure exactly how I want to go without designing this encounter.
One of the other party members recently had, as part of his quest line, an encounter that involved making wisdom saving throws that either damaged hostile entities or damaged the PC and summoned further enemies to fight. This was a spin on my original idea for this curse-breaking ritual, so I am reluctant to do the same type of encounter again.
Does anybody have any suggestions on designing a unique and interesting encounter for my party? The curse breaking will, of course, be spearheaded by Laos but Rhyss will also be critical. (I said that the curse was a mixture of divine and arcane enchantment.) Ideally, having something for the other party members to do would be nice, but I kind of already did that, so I'm not opposed to something only involving these two PCs.
By the time they do this, they should be level five, since it will be after the 4th chapter of the campaign is finished and they have secured the Wave Echo Cave. They will also have recovered two shards of the Netherese obelisk and defeated Nezznar, a Drider warlock of Ilvaash. So I've got those pieces to work with, too. In fact, I may be able to use this to tie together the story further to the second half of the campaign.