Help Me Tailor An Endgame Battle for a Level 15 Party!

[SowZ]

So a story arc is coming to a close.

The setting iss a specific hell the party got sucked into a year ago by trying to kill a demonic summoner. The demons and devils both live in this plane and each has their own cities with lawful evil and chaotic evil damned souls as residents, respectively. In hell, people don't level up, (they are dead and can learn little.) But the PCs were alive and could grow in power so were a strong commodity. Both the Devils and Demons, (who are at war,) tried to recruit them. Instead an ubermensch master diviner imp has been manipulating everyone to reshape hell offered them a deal to spend one year on the surface to grow in strength and then they would be summoned back and would have to kill one devil and one demon. This fulfills his master plan. If they succeed, he will grant each one any favor in his power.

The Demons are individually stronger and are led by the strongest being in this hell. The Devils are greater in number and more organized. It is fairly equal. The Imp has caused both sides to make a major push and started a major battle like hasn't been fought in centuries to draw both sides leaders outside, (in their homes they are too well warded and guarded to be killed.) Both generals must be killed. The Imp will divine when each will be the most alone and when each will be the most vulnerable during the battle and they must decide when to fight each.

I am trying to give a challenging boss fight. The Devil they must kill is the leader of the Devil army and a Horned Devil. He is very brave and will fight to the death, but usually has a number of lesser devils with him and always has his pet Bezekira, (Hellcat.) The Balor is less predictable and leads the demons but is arrogant and has few minions at his side. My PC mortality rate is reasonably high but not obscene so I am not afraid of a death but I would like the party overall to suceed.

The party is an Elven Ranger 12/Sworn Slayer 1/Targeteer 1, a Half-Fiend Human Fighter 10/Ranger 2, an Imp Sorcerer 12, and a Human Rogue 15. They have had a while to prepare for the fight and so will be able to cancel out the worst of the Demonic special abilities. The party is built well but not super optimized. The dual dagger Rogue has highly varying damage as does the Sorcerer. The Ranger is an archer who deals about 110-150 dmg. a turn if all attacks hit with an average of +30 to hit. The Fighter is a dual wielder who deals about 160-200 dmg. a turn with an average of +26 to hit.

How would you recommend tailoring the encounters?

[SowZ]

Yeah, so I have two days. I would welcome help. Otherwise, in addition to the two boss battles I am just going to have demonic low-mid level reinforcements keep showing up until it is a challenge. Tactics to stop said reinforcements will also stop the waves.

[Eldariel]

A Horned Devil, not a Pit Fiend? Meh.

Anyways, what exactly do you want help with? The builds for the monsters, the general setup or tactics or what? Also, how much control do the PCs have over the exact time and location of the engagement and how prepared are the Big Bads?

[Runestar]

One thing I don't like about outsiders is the absence of a higher-cr brute fiend. For bodyguards, consider using 2 or more barbed devils advanced to 18HD. This would put them at large and at cr12. They would have fairly decent hp and attacks. Round out their stats with magical armour, weapons and the spring attack feat tree (expanded in PHB2) so they can move and still make up to 3 attacks.

Because the only SLA they have is greater teleport, they won't be difficult to run. Nor do you have to keep track of the individual SLAs of a dozen different fiends.

Archery can be covered by suitably advanced erineyes.

For spellcasting support, perhaps an ice devil to clutter up the battlefield with ice walls?

For your horned devil, perhaps refeat him into a trip monkey? Swap out his current feats for quicken SLA:fireball, combat reflexes, expertise, improved trip, improved disarm and maybe robilar's gambit.

Not sure what to use for mooks. Legion devils are interesting, but I don't have experience with them at higher lv gameplay.

[SowZ]

A Horned Devil, not a Pit Fiend? Meh.

Anyways, what exactly do you want help with? The builds for the monsters, the general setup or tactics or what? Also, how much control do the PCs have over the exact time and location of the engagement and how prepared are the Big Bads?

I didn't go with a Pit Fiend because it seemed to similar to a Balor in appearance, hehe. Besides, the theme is that Devils are more organizes but the Demons are greater in individual power so the Demon leader will be stronger then the leader of the Devils.

The PCs have literally had eight levels to prepare for this fight. 3/4 have bane, (E. Outsider,) weapons, (this is one of my few non-low magic campaigns,) both melee fighters have lionheart amulets, etc. etc. The Big Bads are prepared for a massive battle, demons ready to fight devils devils ready to fight demons. The Imp who has manipulated this battle into occuring is a master diviner and will tell the party when the enemies will be most alone or when they will be most vulnerable and the PCs can choose when/how to engage but it has to be at some point before or during the battle, (which will start about an hour after the PCs are summoned.)

Both big bads both know about the PCs, (both thought the PCs where working for them at one point but have lost trust,) and one side has sent a couple Bebeliths to kill them and figures that will do the job and the Devil Commander is not worried with all of his troops around him.

The idea I have is that the Balor will have fewer troops but be tougher, (obviouslt,) but the Horned Devil will have better tactics and more guys. To make a challenging and believable fight, what kind of tactics do you think they would use? Also, for the Balor fight, what kind of troops should he have with him to make it challenging, utilize everyone's abilities, but not TPK unless the PCs are unlucky/stupid? Same for the Horned Devil.

Thanks.

[SowZ]

One thing I don't like about outsiders is the absence of a higher-cr brute fiend. For bodyguards, consider using 2 or more barbed devils advanced to 18HD. This would put them at large and at cr12. They would have fairly decent hp and attacks. Round out their stats with magical armour, weapons and the spring attack feat tree (expanded in PHB2) so they can move and still make up to 3 attacks.

Because the only SLA they have is greater teleport, they won't be difficult to run. Nor do you have to keep track of the individual SLAs of a dozen different fiends.

Archery can be covered by suitably advanced erineyes.

For spellcasting support, perhaps an ice devil to clutter up the battlefield with ice walls?

For your horned devil, perhaps refeat him into a trip monkey? Swap out his current feats for quicken SLA:fireball, combat reflexes, expertise, improved trip, improved disarm and maybe robilar's gambit.

Not sure what to use for mooks. Legion devils are interesting, but I don't have experience with them at higher lv gameplay.

All good suggestions, thanks.

[CTrees]

Colossal Half-fiend Gelatinous Cube. "UNLEASH THE HELL CUBE!"

That's all I've got, at the moment. I mean, creating lemure swarms and whatnot would be fun, but the Hell Cube just makes me giggle.