First, if you're a PC of mine and see this then know that it's been a fun game and I'm looking forward to the finale, now go away!
Are you gone? Ok then, moving on:
Hey everyone, I'm wrapping up a Kingmaker game that has gone a completely different direction than the official campaign, and the party is facing their final enemies. I've got 4 PCs left, all at 11th level. They aren't particularly optimized or wimpy, but are balanced out with some pretty good stats and equipment for their level. The characters are a hobgoblin witch, half-elf druid, dwarf inquisitor, and human monk with a dash of ninja. I'm fairly sure that the enemies are going to be quite brutal opponents and give the party a fun, challenging end to a 2 year long campaign, but I'm getting worried about the PC witch and in particular the major hex Ice Tomb trivializing what are supposed to be the two mightiest opponents.
The Witch in question is a pretty effective enemy de-buffer with the hexes Misfortune, Fortune, Evil Eye, Cackle, Flight, and the major hex Ice Tomb. The Ice Tomb hex has a base DC of 23 before possible additional troubles from Misfortune or Evil Eye, de-buff spells, and the like.
The party is level 11, and the big bads of the campaign are a group of demon-possessed enemies which is threatening their nation and the region, and which the group is taking down. The final conflict will involve two of these enemies, a sorceress and a bladesinger (arcane duelist) style bard, who I noticed have rather poor fort saves even with generous stats and equipment. This needs to be a winnable, though hard, fight so I don't want to go higher than CR 13 or so each, and I've had some nightmarishly long fights recently with 8-12 weaker enemies that have proven more annoying to PCs than challenging, so I don't want to give them a swarm of lesser allies. I am willing to modify the big bads slightly, since I haven't revealed full stats to PCs, but they can't be totally redesigned since the party has seen them before and knows some of the things they can do.
Within these limitations I'm happy to listen to advice and follow what I think will fit the enemies best: CR 15-16 hard cap, one major enemy a demon-possessed sorceress of at least 9th level, one major enemy a rapier wielding demon-possessed single blade (rapier when the party saw) and arcane magic using character, less than 6 enemies (counting the two big bads as two of these), and makes sense for the location and flavor (the Abyss and two demon possessed beings in charge). Also, the advice should not include the antagonize feat, summoners, gunslingers, or metamagic rods, since the party can't use any of these things, and the less drastic the measure the happier I am to consider it. Oh, and the final conflict is this Sunday so any advice I get after that point won't help me (though general advice could help lots of others I'm sure).
Thanks in advance for any answers here, I look forward to seeing the responses!