Zardnaar
Legend
So recently my players fought an avatar of Bhaal at level 12. I refluffed a Marilith as the slayer and added some mythic and legendary resistances to homebrew CR13 assassin for the "human" form of Bhaal. Basically they had to kill the slayer to defeat Bhaal's form. The stats below are a scaled down form of what I used for the slayer form. One player correctly identified what creature I was using (only the Marilith gets multiple reactions). It was the 9th encounter that day over 3 sessions. Level 12, divine intervention prayer of healing in combat with a warlock etc. Grinding them down takes a while.
Walking Through It
At these levels things like Heroes Feast and upcast aid become available. Of course my players used both the aid was level 5 via a celestial warlock. Mike Mearls has pointed out the big problems control spells cause in 5E. A CR 13 creature with a weak will save is effectively CR 0. You have the deadly duo of command+ Tashas hideous laughter. The unholy trinity of Hypnotic Patter, Fear and Slow. and the tag team of hold person/hold monster. I had 4 PCs who can cast command and 3 of them could cast hold monster. The monk has access to stunning strike. Missing from the stats below are legendary resistances 4 or 5. Even a +10 con save isn't that reliable vs stunning strikes over a few rounds. My 400+ hp combo "slayer-Bhaal" Lasted 5 rounds and the PCs were basically spent by the end of it. After 8 previous combats. +8 wisdom save with advantage is very good by 5E standards. Then you realize DCs are in the 17-20 range and theres 4 or 5 PCs all with stunlock abilities and nova potential.
Vs the wisdom targeting cheese there is a solution in 5.5 MM. Smart PCs would take spells that target intelligence. Note the Mariliths +4 int save. That's impressive by 5E standards. That solution is the Rakshasa. It has greater Magic Resistance. It plan ol shuts down every single save or suck spell in the game. That leaves PC nova abilities. You could plan old increase the HP. I suggest doubling it but its arguably already to damn high already. Descent into Avernus has the unstoppable mechanics. Blow your reaction to negate damage. A version of that ability appeared in Baldurs Gate 3. Orin has Unstoppable 12. I thought it was an interesting combo with its reactive ability.
But Zard you evil nasty DM you took away the players abilities!!! So what guess what happened? The Monk gets six attacks a round, the Ranger got 2 or 3, Warlock 3 if there was a fighter in the party I'm looking at potentially 7. Even unstoppable doesn't do much vs that. Sorcerer has Summon Dragon the Cleric had summon celestial and spirit guardians, the warlock has Spirit Shroud and a +2 greatsword with abilities. With the Bhaal form the fight lasted 5 rounds total or so. No they're level 13. I'm staring down the barrel of Conjure Celestial now. Spirit Guardians on steroids. "Kate" did a lot of damage focus fire on the Ranger but 5 PCs laying into her it didn't take long. "mythic" bhaal; appeared but even with mythic and legendary actions it didn't matter to much. They were more or less tanked at the end though and a couple of them were very low on HP. I left Kate CR as is. "Bhaal" was similar to the CR 8 assassin, double HP, unstoppable, extra attack, legendary actions, etc. Kates a watered down version of what I used its more of a base where I think a CR 16 needed to be not a definitive statement.
Walking Through It
At these levels things like Heroes Feast and upcast aid become available. Of course my players used both the aid was level 5 via a celestial warlock. Mike Mearls has pointed out the big problems control spells cause in 5E. A CR 13 creature with a weak will save is effectively CR 0. You have the deadly duo of command+ Tashas hideous laughter. The unholy trinity of Hypnotic Patter, Fear and Slow. and the tag team of hold person/hold monster. I had 4 PCs who can cast command and 3 of them could cast hold monster. The monk has access to stunning strike. Missing from the stats below are legendary resistances 4 or 5. Even a +10 con save isn't that reliable vs stunning strikes over a few rounds. My 400+ hp combo "slayer-Bhaal" Lasted 5 rounds and the PCs were basically spent by the end of it. After 8 previous combats. +8 wisdom save with advantage is very good by 5E standards. Then you realize DCs are in the 17-20 range and theres 4 or 5 PCs all with stunlock abilities and nova potential.
Vs the wisdom targeting cheese there is a solution in 5.5 MM. Smart PCs would take spells that target intelligence. Note the Mariliths +4 int save. That's impressive by 5E standards. That solution is the Rakshasa. It has greater Magic Resistance. It plan ol shuts down every single save or suck spell in the game. That leaves PC nova abilities. You could plan old increase the HP. I suggest doubling it but its arguably already to damn high already. Descent into Avernus has the unstoppable mechanics. Blow your reaction to negate damage. A version of that ability appeared in Baldurs Gate 3. Orin has Unstoppable 12. I thought it was an interesting combo with its reactive ability.
But Zard you evil nasty DM you took away the players abilities!!! So what guess what happened? The Monk gets six attacks a round, the Ranger got 2 or 3, Warlock 3 if there was a fighter in the party I'm looking at potentially 7. Even unstoppable doesn't do much vs that. Sorcerer has Summon Dragon the Cleric had summon celestial and spirit guardians, the warlock has Spirit Shroud and a +2 greatsword with abilities. With the Bhaal form the fight lasted 5 rounds total or so. No they're level 13. I'm staring down the barrel of Conjure Celestial now. Spirit Guardians on steroids. "Kate" did a lot of damage focus fire on the Ranger but 5 PCs laying into her it didn't take long. "mythic" bhaal; appeared but even with mythic and legendary actions it didn't matter to much. They were more or less tanked at the end though and a couple of them were very low on HP. I left Kate CR as is. "Bhaal" was similar to the CR 8 assassin, double HP, unstoppable, extra attack, legendary actions, etc. Kates a watered down version of what I used its more of a base where I think a CR 16 needed to be not a definitive statement.
"Kate" Marilith of Bhaal
Large Fiend (Demon)) chaotic evil
Armor Class 16 Intiative +15
Hit Points 220 (21d10d8+105
Speed40 ft.
Str 18 (+4) Save +9 , Dex 20 (+5) Save +5, Con 18 (+4) Save+10, Int 18 (+4) Save +4, Wis 16 (+3) Save +8, Cha 20 (+5) Save +10
Skills, Perception +10,
Resistances Cold,Fire, Lightning
ImmunitiesPoison,Poisoned
SensesTruesight120' passive perception 18
LanguagesAbyssal;Telepathy 120'
Challenge16(15000 XP, PB +5)
Traits
Demonic Restoration (as page 204 MM)
Greater Magic Resistance (as Rakshasa pg 253 mm)
Reactions. Kate can take 1 reaction on every turn (MM pg 204)
Actions As MM pg 205
Reactions add
Unstoppable(12/day). Kate reduces the damage it takes from an attack to 0.
Armor Class 16 Intiative +15
Hit Points 220 (21d10d8+105
Speed40 ft.
Str 18 (+4) Save +9 , Dex 20 (+5) Save +5, Con 18 (+4) Save+10, Int 18 (+4) Save +4, Wis 16 (+3) Save +8, Cha 20 (+5) Save +10
Skills, Perception +10,
Resistances Cold,Fire, Lightning
ImmunitiesPoison,Poisoned
SensesTruesight120' passive perception 18
LanguagesAbyssal;Telepathy 120'
Challenge16(15000 XP, PB +5)
Traits
Demonic Restoration (as page 204 MM)
Greater Magic Resistance (as Rakshasa pg 253 mm)
Reactions. Kate can take 1 reaction on every turn (MM pg 204)
Actions As MM pg 205
Reactions add
Unstoppable(12/day). Kate reduces the damage it takes from an attack to 0.
