Marilith
Large fiend, chaotic evil
Armor Class 16 (natural armor)
Hit Points 220 (21d10 + 105)
Speed 40 ft., swim 20 ft., climb 40 ft.
str
18 (+4)
dex
20 (+5)
con
20 (+5)
int
18 (+4)
wis
16 (+3)
cha
20 (+5)
Saving Throws Str +9, Con +10, Wis +8, Cha +10
Skills Perception +8
Damage Resistances cold, fire, lightning
Damage Immunities poison
Condition Immunities poisoned
Senses truesight 120 ft., passive Perception 18
Languages Abyssal; telepathy 120 ft.
Challenge 16 (15,000 XP)
Demonic Restoration. If the marilith dies outside the Abyss, its body dissolves into ichor, and it gains a new body instantly, reviving with all its Hit Points somewhere in the Abyss.
Magic Resistance. The marilith has Advantage on saving throws against spells and other magical effects.
Reactive. The marilith can take one Reaction on every turn of combat.
Actions
Constrict. Strength Saving Throw: DC 17, one Medium or smaller creature the marilith can see within 5 feet. Failure: 15 (2d10 + 4) Bludgeoning damage. The target has the Grappled condition (escape DC 14), and it has the Restrained condition until the grapple ends.
Multiattack. The marilith makes six Pact Blade attacks and uses Constrict.
Pact Blade. Melee Attack Roll: +10, reach 5 ft. 10 (1d10 + 5) Slashing damage plus 7 (2d6) Necrotic damage.