Marilith
Large Fiend (demon), chaotic evil
15,000 XP
Special Abilities
Magic Resistance
The marilith has advantage on saving throws against spells and other magical effects.
Magic Weapons
The marilith's weapon attacks are magical.
Reactive
The marilith can take one reaction on every turn in combat.
Actions
Multiattack
The marilith can make seven attacks: six with its longswords and one with its tail.
Longsword
Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) slashing damage.
Tail
Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 15 (2d10 + 4) bludgeoning damage. If the target is Medium or smaller, it is grappled (escape DC 19). Until this grapple ends, the target is restrained, the marilith can automatically hit the target with its tail, and the marilith can't make tail attacks against other targets.
Teleport
The marilith magically teleports, along with any equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.
Variant: Summon Demon (1/Day)
The demon chooses what to summon and attempts a magical summoning.
A marilith has a 50 percent chance of summoning 1d6 vrocks, 1d4 hezrous, 1d3 glabrezus, 1d2 nalfeshnees, or one marilith.
A summoned demon appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can't summon other demons. It remains for 1 minute, until it or its summoner dies, or until its summoner dismisses it as an action.
Quick Reference
Running This Encounter
A Marilith is a cunning demon general that leads from the front with confidence. Use its high AC and mobility to keep it in the thick of combat, repositioning frequently with its movement speed. Have it coordinate with lesser demons or cultists to create action economy pressure. Use its spell-like abilities (particularly Wall of Fire and Fire Storm) to control the battlefield and force difficult choices.
Combat Tactics
The Marilith uses its multiple weapon attacks to focus fire on the party's strongest martial combatants while maintaining distance when needed. It casts Fireball and other area spells to damage clustered enemies, then engages melee threats directly with its six scimitars. It prioritizes disabling spellcasters through positioning and will attempt to flee if reduced below 50 HP.
Environment & Setting
An infernal war chamber, demonic temple, or deep dungeon throne room where the demon can utilize vertical space and pillars for tactical positioning. The area should have enough space for the creature's 40-foot movement and include environmental hazards like lava pits or magical wards.