CR Check for 2 Monsters

[Emongnome777]

I've created a new monster as part of a side quest that is based off of the Murder in Baldur's Gate adventure (happens 7 years later). I can provide more details about the "why" of the creature, but for now, here's its stats. I'm mostly interested to see if it lines up with its CR or if I need to tweak it in some way. Any other general comments that help improve it would be great as well.

VENEMIR
Large monstrosity, chaotic evil
Armor Class: 14 (natural armor)
Hit Points: 102 (12d10+36)
Speed: 40 ft
Str 18 (+4) Dex 17 (+3) Con 16 (+3) Int 11 (+0) Wis 15 (+2) Cha 16 (+3)
Saving Throws Con +6, Wis +5, Cha +6
Skills Perception +5
Damage Resistance bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities acid, poison
Condition Immunities charmed, frightened, poisoned
Senses darkvision 60 ft., passive Perception 15
Languages Common
Challenge 8 (3,900 xp)

--TRAITS--
Bhaal's Immortality
If Vesemir dies, he immediately transforms into a mist that floats away and reforms into his humanoid form at his laboratory. That mist travels at 30 feet per round.
Regeneration
Venemir regains 10 hit points at the start of its turn. If Venemir takes radiant or fire damage, this trait doesn't function at the start of his next turn.
Stench
Any creature that starts its turn within 5 feet of Venemir must succeed on a DC 14 Constitution saving throw or be poisoned until the start of its next turn. On a successful saving throw, the creature is immune to Venemir's stench for 24 hours.
Magic Resistance
Venemir has advantage on saving throws against spells and other magical effects.

--ACTIONS--
Multiattack
Venemir makes two slam attacks.
Slam
Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 11 (2d6 + 4) bludgeoning damage plus 5 (2d4) acid damage.
Acid Breath (Recharge 5-6)
Venemir spews acid in a 10-foot cone. Each creature in that cone must make a DC 14 Dexterity saving throw, taking 33 (6d10) acid damage on a failed save, or half as much damage on a successful one.

VENEMIR (ENHANCED)
Large monstrosity, chaotic evil
Armor Class: 15 (natural armor)
Hit Points: 119 (14d10+42)
Speed: 40 ft
Str 20 (+5) Dex 17 (+3) Con 16 (+3) Int 11 (+0) Wis 15 (+2) Cha 16 (+3)
Saving Throws Con +7, Wis +6, Cha +7
Skills Perception +6
Damage Resistance bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities acid, poison
Condition Immunities charmed, frightened, poisoned
Senses darkvision 60 ft., passive Perception 16
Languages Common
Challenge 10 (5,900 xp)

--TRAITS--
Bhaal's Immortality
If Vesemir dies, he immediately transforms into a mist that floats away and reforms into his humanoid form at his laboratory. That mist travels at 30 feet per round.
Regeneration
Venemir regains 15 hit points at the start of its turn. If Venemir takes radiant or fire damage, this trait doesn't function at the start of his next turn.
Stench
Any creature that starts its turn within 5 feet of Venemir must succeed on a DC 15 Constitution saving throw or be poisoned until the start of its next turn. On a successful saving throw, the creature is immune to Venemir's stench for 24 hours.
Magic Resistance
Venemir has advantage on saving throws against spells and other magical effects.

--ACTIONS--
Multiattack
Venemir makes two slam attacks.
Slam
Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 14 (2d8 + 5) bludgeoning damage plus 7 (2d6) acid damage.
Acid Breath (Recharge 5-6)
Venemir spews acid in a 15-foot cone. Each creature in that cone must make a DC 15 Dexterity saving throw, taking 44 (8d10) acid damage on a failed save, or half as much damage on a successful one.

--BONUS ACTIONS--
Misty Teleport
Vesemir can transform into a mist and teleport up to 30 feet, reforming at his destination.

--REACTIONS--
Misty Defense
Upon getting hit with an attack, Vesemir can transform into a mist and teleport to a space up to 10 feet away, reforming at his destination. This teleport negates the hit. He then can make one slam attack against a creature in range.

[Yakk]

32 base DPR
+4 main attack stat
14 AC
15ish regen (pcs will figute it.out)
102 HP
MR, 3 saves
stench
2 target aoe @/fight 33 damage save half (33*2-32=34 extra damage, 1.5/fight)
Imminities worth, say 10% hp buff at most
treating reform as a story thing

I'll put stench at 2 ac, so 20 effective AC
117 * 1.1 = 129 hp effective
3 round damage of 32*3+34*1.5 96+34+17=147, or 49 dpr average
49/12+129/32+20/4+4/4-6.5 is 7.6 cr.

So right ballpark.

[Yakk]

Upgrade has 26 extra effective HP, 1 more AC, 1 more atk, 10 more DPR base, 18 more burst (so 16 more dpr total), misty syep, and that reaction.

Reaction nullifies one hit (say 40 hp over fight?) and does 21 dpr.

66/32+1/4+1/4+37/12
that is like +5 CR, not +2.

[sandmote]

I'll treat the stench as +1 to AC; it isn't likely to affect ranged PCs and a lot of melee PCs can make a Con save reasonably well. The formal rules in the DMG get me the following:

The original version has a defensive CR of 9 and an offensive CR of 6, for a total of 8. That said the resistances are likely to be ignorable; if the PCs all have magical weapons the effective defensive (and total) CRs drop to 6.

The Enhanced version is weirder, due to the resistance table having a break point between CR 10 and CR 11. Offensive CR is 12, but the defensive CR is 13 if using the multiplier for CR 5-10 creatures and 11 if using the multiplier for CR 11-16 creatures. That's a written CR of 12, I guess. If all the PCs have magic weapons though, effective defensive CR drops to 10.

The above also assumes that Misty Defense resolves after Venemir has taken the damage; if it lets him avoid damage then effective hit points should be higher by however much damage you expect him to avoid. I also expect that using Misty Teleport then walking away can help him avoid damage from Melee focused PCs.

[Yakk]

The above also assumes that Misty Defense resolves after Venemir has taken the damage; if it lets him avoid damage then effective hit points should be higher by however much damage you expect him to avoid. I also expect that using Misty Teleport then walking away can help him avoid damage from Melee focused PCs.
It is "This teleport negates the hit. He then can make one slam attack against a creature in range."

The hit is negated.

[Emongnome777]

Thanks so much for the quick responses. These are very helpful. I know to use the table in the DMG to get a CR, but figuring out how the other stuff affects it was kinda difficult. Let me address a few comments:

Bhaal's Immortality is totally a story element. It comes back (enhanced) and the party will have a means to permanently kill it that second time.

The B/P/S resistance is mostly story as well. The group will have magic equipment by then, but the resistance is a story element as it reflects the difficulty in others dealing with it prior to this point (it keeps coming back stronger). The regeneration is a similar effect, requiring others to use torches to deal with it. The party that will be fighting it has a dragon sorcerer (gold), so fire damage will be easy to come by.

In short, the party deals with the immortality using a blade covered in a viscous elixir, which removes it's immortality for up to 10 rounds. When that happens, I thought it would be fitting that the misty defense and misty teleport also be dropped (since it won't turn to mist post-death). Well, I was going to keep the attack of misty defense, just drop the teleport part.

Thanks again. I tried to make things that seemed most fitting to the creature for the backstory elements, but some of it seems overkill, like the 3 save proficiencies. May tamp down on some of that. Are there any suggestions on making these two more inline with CR 8 & 10 creatures?