CapnZapp
Legend
Just to throw it out there, my players just cleaned out a Zhentarim post overrun with demons, and I thoght you might find it useful with some real play data.
This is a location I've whipped up myself to replace purely random wandering monsters when travelling towards Mantol-Derith in Out of the Abyss.
The most pertinent thing you need to know without needless spoilers are:
- the adventure offers magical attacks to all fightery types; meaning resistance to non-magical weapons as a thing to worry about is over
- the adventure supplies NPCs in droves. While most of these are individually so much weaker than the PCs that they would be a liability, they're using one Knight (with a Sun Blade), one Veteran (with a magical but unspectacular weapon) and one Druid (as a steeder mount) in the following encounters.
- feats and MC is on
The party consists of:
* Female human Ftr7 (EK) with a focus on speed and mobility; two-weapon fighting
* Male elf Mnk7 (WoS) with very useful teleportation and stunning strike
* Male halfling Ftr6/Rng1 (BM) testing the SS/CE feat combo
* Male human Clr7 (Tempest) leaning towards tanking and melee, rather than spells or healing
* Female tiefling Wrl7 (Fiend/Chain) getting tremendous scouting use out of her familiar
The foes were (in order; one line per combat):
2 Vrocks (only three characters)
1 Barlgura and a dozen Manes (the other characters)
1 Glabrezu, 1 Hezrou, 6 Babaus* (this was the main event)
1 Priest, 3 Shadow Demons (with the Veteran NPC as a stand-in for the Monk)
1 Hezrou
Then they cleaned up one insane Veteran, one Vrock, a couple more Barlguras, but I simply narrated that.
Only the Glabrezu fight could dent the party. Thee was never any real doubt the party would win, but the demons did manage to bloody one character, and one NPC and did down the Monk (power word stun plus hezrou fragging still equals chardown
I supposed the DMG would call that a "deadly" result, but in my vocabulary I want to reserve that category for a combat where there is actual risk of death. With "death" meaning "the player has to generate a new character, because the old one is dead".
With a cleric having prepared Revivify this combat was pretty far from that kind of "deadly". It was "challenging" though, which was rather the point - everyone was pleased; I managed to get that "uh oh we're doomed" look on their faces that slowly (read "rather quickly") turned into the grins players have when they smell blood (and victory).
After the Glabrezu fight, the monk left the field; the player brought in the Veteran NPC as a sub. This was because taking a short rest would have meant retreat, since there was still lots of demonic noise in surrounding rooms. And since the other PCs needed only a round or two for a healing potion or spell, but were basically unwounded, they wanted to press on.
I haven't even checked the xp totals or challenge ratings. I just feel good, managing the balance between a trivial and a lethal fight, and the balance between an anticlimactic and a boringly slow fight.
Next session I plan to give the Mob Attacks a whirl - the idea is to see if five dozen or so Gnolls can faze the heroes through sheer numbers. It remains to be seen if my players appreciate the "cheating going on" with those rules, even as I modify them to include a d20 roll per mob (instead of one automatic hit each round).
Zapp
PS. If you're interested, I used this map:
https://rpgcharacters.wordpress.com/2010/07/02/friday-map-the-winter-fortress/
(if you like maps, you'll like this site)
The Vrocks sat in the secret corridor to the right, boringly torturing some hapless Zhent. They would have attacked the characters in the rear, had the party not fought them down there.
The main Glabrezu fight was in the main hall (with the staircase, to the left of the central cavern). The party hacked themselves through the gate, so the demons had prepared. I didn't bother with summoning, but placed more than the initial four Babous I had planned.
The Priest defended an abyssal rift that slowly produced new demons; which I placed in the battlement overlooking the dungeon passage (to the lower left), allowing the party to start the encounter by spotting the sickly unnatural lights of the rift to play through the arrowslits. The mad priest was the one making sacrifices and pacts and stuff to create the rift, but was obviously not the main foe. He did suffer the indignity of being insta-taken down by a bolt with Drow Sleep Poison!
The lone Hezrou came through the rift by random (high) roll, but too late to do anything. In fact, the party completely neutered him by repelling eldritch blasts and Wind Blast - he could never close to melee.
*) The Babau isn't in the MM, but I needed a good damage-dealer in the CR 5ish range that wasn't the (rather impotent) shadow demon. I ended up with this.
Babau: 56 hp, AC 14, 40% summon Babau; 2 Claws: +5 1d6+3, +3d6 flank attack; Protective Slime: 1d8 acid damage or –1 perm penalty when touching or attacking Babau in melee. Magic weapons get DC 12 Reflex save.
The babau's didn't get to wreak the havoc their stats allow them to, but that's the expected result - if they do, the party is toast. The difficult terrain from Spirit Guardians bought the party the crucial round. Though one babau did hit the AC 20 Cleric with one sneak crit for a respectable 8d6+3 damage!
The party was quick to realize the Babau isn't a good choice for a melee slicer and dicer; the fighter and the monk would be hard pressed to deal more damage than they would have taken themselves (three attacks inflict 3d8 acid damage; not to mention how you end up with corroded stumps for gear).
This is a location I've whipped up myself to replace purely random wandering monsters when travelling towards Mantol-Derith in Out of the Abyss.
The most pertinent thing you need to know without needless spoilers are:
- the adventure offers magical attacks to all fightery types; meaning resistance to non-magical weapons as a thing to worry about is over
- the adventure supplies NPCs in droves. While most of these are individually so much weaker than the PCs that they would be a liability, they're using one Knight (with a Sun Blade), one Veteran (with a magical but unspectacular weapon) and one Druid (as a steeder mount) in the following encounters.
- feats and MC is on
The party consists of:
* Female human Ftr7 (EK) with a focus on speed and mobility; two-weapon fighting
* Male elf Mnk7 (WoS) with very useful teleportation and stunning strike
* Male halfling Ftr6/Rng1 (BM) testing the SS/CE feat combo
* Male human Clr7 (Tempest) leaning towards tanking and melee, rather than spells or healing
* Female tiefling Wrl7 (Fiend/Chain) getting tremendous scouting use out of her familiar
The foes were (in order; one line per combat):
2 Vrocks (only three characters)
1 Barlgura and a dozen Manes (the other characters)
1 Glabrezu, 1 Hezrou, 6 Babaus* (this was the main event)
1 Priest, 3 Shadow Demons (with the Veteran NPC as a stand-in for the Monk)
1 Hezrou
Then they cleaned up one insane Veteran, one Vrock, a couple more Barlguras, but I simply narrated that.
Only the Glabrezu fight could dent the party. Thee was never any real doubt the party would win, but the demons did manage to bloody one character, and one NPC and did down the Monk (power word stun plus hezrou fragging still equals chardown

I supposed the DMG would call that a "deadly" result, but in my vocabulary I want to reserve that category for a combat where there is actual risk of death. With "death" meaning "the player has to generate a new character, because the old one is dead".
With a cleric having prepared Revivify this combat was pretty far from that kind of "deadly". It was "challenging" though, which was rather the point - everyone was pleased; I managed to get that "uh oh we're doomed" look on their faces that slowly (read "rather quickly") turned into the grins players have when they smell blood (and victory).
After the Glabrezu fight, the monk left the field; the player brought in the Veteran NPC as a sub. This was because taking a short rest would have meant retreat, since there was still lots of demonic noise in surrounding rooms. And since the other PCs needed only a round or two for a healing potion or spell, but were basically unwounded, they wanted to press on.
I haven't even checked the xp totals or challenge ratings. I just feel good, managing the balance between a trivial and a lethal fight, and the balance between an anticlimactic and a boringly slow fight.

Next session I plan to give the Mob Attacks a whirl - the idea is to see if five dozen or so Gnolls can faze the heroes through sheer numbers. It remains to be seen if my players appreciate the "cheating going on" with those rules, even as I modify them to include a d20 roll per mob (instead of one automatic hit each round).
Zapp
PS. If you're interested, I used this map:
https://rpgcharacters.wordpress.com/2010/07/02/friday-map-the-winter-fortress/
(if you like maps, you'll like this site)
The Vrocks sat in the secret corridor to the right, boringly torturing some hapless Zhent. They would have attacked the characters in the rear, had the party not fought them down there.
The main Glabrezu fight was in the main hall (with the staircase, to the left of the central cavern). The party hacked themselves through the gate, so the demons had prepared. I didn't bother with summoning, but placed more than the initial four Babous I had planned.
The Priest defended an abyssal rift that slowly produced new demons; which I placed in the battlement overlooking the dungeon passage (to the lower left), allowing the party to start the encounter by spotting the sickly unnatural lights of the rift to play through the arrowslits. The mad priest was the one making sacrifices and pacts and stuff to create the rift, but was obviously not the main foe. He did suffer the indignity of being insta-taken down by a bolt with Drow Sleep Poison!

The lone Hezrou came through the rift by random (high) roll, but too late to do anything. In fact, the party completely neutered him by repelling eldritch blasts and Wind Blast - he could never close to melee.
*) The Babau isn't in the MM, but I needed a good damage-dealer in the CR 5ish range that wasn't the (rather impotent) shadow demon. I ended up with this.
Babau: 56 hp, AC 14, 40% summon Babau; 2 Claws: +5 1d6+3, +3d6 flank attack; Protective Slime: 1d8 acid damage or –1 perm penalty when touching or attacking Babau in melee. Magic weapons get DC 12 Reflex save.
The babau's didn't get to wreak the havoc their stats allow them to, but that's the expected result - if they do, the party is toast. The difficult terrain from Spirit Guardians bought the party the crucial round. Though one babau did hit the AC 20 Cleric with one sneak crit for a respectable 8d6+3 damage!

The party was quick to realize the Babau isn't a good choice for a melee slicer and dicer; the fighter and the monk would be hard pressed to deal more damage than they would have taken themselves (three attacks inflict 3d8 acid damage; not to mention how you end up with corroded stumps for gear).