Name: The whole party. Justin Verres, Xanthippe Euphram, Ray Banashim, Talnar, and Reynard Trellers.
Races: Justin was an Aasimar, everyone else was human.
Justin - Battle Oracle 16
Xan - Bladebound Magus 16
Ray - Witch 16
Talnar - Druid 16
Reynard - Ecclesitheurge Cleric 16
Adventure: The Witch Queen's Revenge
Catalyst: Queen Elvanna is brutal.
The Gory Details: This happened last Friday night, I'm just getting over it. The players are in a worse state and I'm worried that it might take a while for them to forgive me.
If I'm going to blame the victims here, I had to say that the party was poorly prepared. Their spell selection was questionable considering that they must have known that they were going up against a powerful caster. No Freedom of Movement. No Silence. Not much Dispel Magic. One PC had True Sight memorized, but not cast until after the fight started. There are a lot of useful tools for dealing with casters. The party inexplicably decided not to prepare them.
Looking at how Queen Elvanna prepares for the fight, I had a bad feeling even going into this. To put it mildly (and to avoid spoilers), she's probably the most powerful Witch alive (except of course her mother ...), she knows you're coming, she's been watching you, and she can bring it like nothing else in the game can.
The Party ran up the corridor as a group, so everyone got hit by (what's on the door). She actually rolled poorly on the initiative. Most of the party charged into her room and engaged her minions. She was able to get almost everyone within her Polar Midnight. Her Rime polar midnight. Infused with Numbing Chill. It took the party several rounds just to get out of there (and freeing some of their comrades who were frozen). Meanwhile, she spent the rest of the fight blasting the players with her most powerful spells while the Demodands just cast Greater Dispel Magic on whatever PC was irritating them.
It turns out her most powerful spells REALLY HURT. Polar Ray on Talnar when he came too close. Mass Suffocation. Wail of the Banshee. The party was resilient, but the continual spell battering eventually broke them down. Eventually, she ended the fight with a Split Major Hex Frost Tomb, putting down the last two standing party members.
The players were (understandably) upset. But despite their complaints, I don't think this fight is unwinnable. It's a tough fight, sure! Elvanna isn't the Witch Queen of Irrisen by accident. But it's definitely not a fight that you want to have while poorly prepared. PCs can overpower most fights, that's not really an option here.
At some point in the future, I might run Reign of Summer. These PCs are down but not all out - Talnar and Reynard are definitely dead, but the dead can become vengeful ghost NPCs. Ray is dead, but she used a contingency to meld her spirit into her familiar. Maybe she can keep that up indefinitely. Xan and Justin are trapped in a Frost Tomb, and it's entirely possible that they'll stay that way, possibly on display as statues in Whitethrone ... until some plucky adventurers free them in a daring raid.
We'll be playing something else, with a different DM, for a while. But this might have the makings of a fun game once tempers are cooled.