Help me challenge a 15th level party with some evil outsiders

[Trainwreck]

I have a party consisting of:

--Archery-based paladin with a seeking bow.
--Summoner who mostly stays out of battle, summons whatever is appropriate, and casts dazing walls of fire.
--Witch who has taken on healing duty (divine healing has been shut off temporarily in this world) and often focuses on support spells.
--Dragon disciple/sorceror who alternates between acid damage, melee, and mobility (can become a specter as a free action)
--Oracle with advanced and celestial template added to make up for a weaker build who front lines and smites.
--Fighter who can one-shot most bad guys if she gets off a full-round attack, but has the usual fighter weaknesses.

They're all 15th level and are a level or two stronger than that due to some ability score boosting boons and extra feats they've picked up, plus they have a couple of god-level boons to cash in if I overdo it and end up challenging them too much (basically, can get a miracle or two, if needed).

They're trying to stop an incursion from the evil planes (demons, devils and daemons all are on the same team in the campaign I'm running), so any combination can show up together.

I want to really push them, but of course, don't want to overdo it.

So far, I've come up with a few Kalavakas demons with the disarm feats to steal weapons and teleport away (they have access to an armory after the battle), and I thought it would be fun to have a few mid-level creatures with some class levels, along with some decent minions to keep the summoned creatures busy.

Anyone feel like helping me come up with bad guys?

[Doomed Hero]

Belier Devil.

Which of your players has the worst Will save?

These guys can Plane Shift to the Etherial, watch the party invisibly, pick the best time and target, lead with Dispel Magic to get rid of any will-boosting enchantments or protective items, and then Dominate them.

If done right this could be done without the rest of the party even knowing. Consider a first command of "act normally, but do not reveal me or my control of you in any way."

Also consider that Dominate Person for them lasts 17 days, so the belier could already have quite a few folks under its sway. Nothing like a small army of mind controlled innocents to muck up an encounter.

Then it just leaves when the tide starts to turn. Yay for recurring villains.

[Trainwreck]

The Belier sounds pretty cool. Having a party member dominated isn't all that fun, though. I will probably have it target one of the NPC's who are assisting the party.

Thanks for the suggestion.

Obviously, any other ideas will be welcome.

[Rycaut]

I haven't tried building this but one that comes to mind would be a group of Babau demons with class levels either as Slayers or Rogues (Unchained). Probably wouldn't kill your party outright - but they would like be a challenging encounter with the right tactics and possibly some other support creatures/casters?

at will Teleport as well as Dispel Magic could result in some interesting tactics - and you might look at whether they would have the feats to have dispelling critical or something similar.

(you could also look at the obvious adding Assassin prestige class levels to them - but I think the newer Slayer class or unchained rogue would actually be a more effective build) - and in either case I would play up the poison use - a demon likely has access to nasty poisons... as well as the stealthy, stalker killer angle - have the babau's track and follow the party - stalking them perhaps over the course of multiple encounters in an adventure (using greater teleport to escape as needed)

I think to get the CR to a challenging point you are likely looking at 12 or more class levels but I haven't done the math - but it should be enough to make what would usually be a cakewalk for Level 15 characters (CR6 creatures) be a very real challenge - provided there are enough of them.

I'd probably suggest addend 12-13 levels of rogue or slayer to the babau's (remember that you also boost their stats by +4, +4, +2, +2, +0, -2 as appropriate - and then further for for level 4, 8 and 12. 12-13 levels would give you a bunch of feats and rogue talents to work with and aboost to hd, BAB, saves etc. Overall I think if you then used 4 of them, possibly more you are looking at a CR19+ encounter fairly easily (may be higher actually but sounds like your PC's are pretty strong, if you think it would be too high then drop a level or two)

[Trainwreck]

The slayer-Babau sounds like it could be pretty powerful. The only thing I'm worried about is that their tactics (teleport in, sneak up, inflict massive damage) doesn't allow the party much opportunity to counter it.

I'd be afraid the scenario would just start out with the party taking lots of damage out of the blue.

Something a little less sneaky allows the party the chance to figure out a strategy for countering the threat. I might build a couple of them up at slightly lower level just to constantly harass and skirmish the party.

Thanks, and keep the ideas coming. :)

[Rycaut]

You could have the babau's tracking the party and ambush them then teleport out - teleporting in would be hard without a means of a scrying - but fleeing would mean the party now has a dangerous foe to prepare for and/or seek out. They likely would drop darkness as well (as a GM I would probably let a demon qualify for a feat usually limited to tieflings and let them get the blinding sneak attack feat but that could be overkill)

Remember as well that they can summon basic babau as fodder - so that can give the party some warning while the slayers observe the party's tactics. I think done right it could be a multiple encounter threat. (Either rogues or slayers would be potentially devastating - though I've learned not to pull punches with high level play)

[Doomed Hero]

Sounds like our players are about CR 17. Here's all the CR 17 monsters.

There's quite a few good ones.

If you want to be nasty give a Succubus 10 levels of Antipaladin or Swashbuckler.

If you want to be even more nasty, adapt This Guy.

[Trainwreck]

Doomed Hero wrote:

If you want to be even more nasty, adapt This Guy.

Well, now I have a homework assignment, looking up all the abilities of that antipaladin.

Still need to figure out a good caster to go along with him/her. Thanks for the help.