By Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging encounters against a Marilith
Note: This has been prepared utilizing only the 5E Core Rules. Additional source material can be found in the book Mordenkainen’s Tome of Foes.
The Marilith can be found in the Monster Manual page 61. Additional information regarding Demons is in the Monster Manual starting on pages 50-65.
I strongly suggest that you read this section fully prior to utilizing one of these creatures as monster. Demons are creatures of chaos, and while this article will describe them in general terms, every demon is unique.
Demons in General
Demons are creatures of vile darkness, they have no compassion, no empathy, no inhibition, no restraint, and if they find themselves in power over you, no mercy.
Demons have no fear, as they know that to be destroyed anywhere in the multiverse is simply to be reborn on its home plane. It is only by journeying to the portion of Hell called the Abyss can you seek out and destroy a demon forever. Still, Demons respect power, and they avoid the destruction that can send them back. They will speak with and deal with those they know have the power to destroy their current demonic form.
Demons exude an aura of corruption around themselves, twisting and warping the natural into something foul. Animals will avoid a place where the demonic taint is present. It often manifests in the form of a foul stench that won’t go away, areas of bitter cold, permanent shadows, or twisted vegetation.
Demons are creatures of true Evil, but they are also creatures of great power and great knowledge. Among the masters of lore are those who have discovered the fact that every demon possesses a unique individual name. This TRUE NAME consists not only of the letters and language, it also consists of cadence and inflection, tone and volume.Masters of Lore who believe that they have learned the true name of a demon may attempt to summon it to the mortal world, perhaps to question it, perhaps to make some demand. Rituals involved in summoning a demon essentially try to create a little “Hell on Earth” and thus entice the demon to make the journey.
Unless the summoner has prepared every aspect of their ritual to perfection and pronounces the name of the Demon properly, the summons will either fail, or worst, succeed but without any controls over this malign entity in place.
A demonic summoning unchecked can bring in a catastrophe that the dark legends speak of “A Demonic Invasion”. The summoned demon, having escaped from control, will begin to summon others of its ilk, inflicting great devastation.
The Marilith
The Mariliths are the Battle-Captains at the head of a Demonic Horde. Acknowledged for their skill in warfare and tactical prowess, all demons know that to be commanded by a Marilith is to create greater destruction. The Marilith have personal power and directed prestige that enables to assume command of many lesser demons.
Experts in the arts of war, the Marilith is also a formidable killing machine, with each of its six arms and the tail making independent attacks each round. Seeing one in action would cause all but the most stouthearted warrior to flee.
Step 1) Let’s Review what we know about the Marilith
Marilith are Large Fiends with the body of a snake and the torso of a humanoid female with six arms. The humanoid portion of the demon is malleable and will change depending on the desire of the demon. Millennia of experience has taught the Marilith that men have a hard time fighting a creature that is beautiful.
Physically, Marilith are Strong (+4), Dexterous (+5) and Tough (+5).Mentally, Marilith are Intelligent (+4), Strong Willed (+3) and have an amazing presence (+5).
Created to be master combatants, the Marilith are proficient in many saving throws: Str +9, Con +10, Wis +8, Char +10.Marilith are Resistant to Damage from Non-Magical weapon attacks (Bludgeoning, Piercing, Slashing), and are also resistant to Cold, Fire and Lightning based damage.
Marilith are immune to poison and the poisoned condition.
Marilith have Truesight 120 feet, and a passive perception of 13.Marilith speak Abyssal but may converse telepathically with anyone within 120 feet.
Marilith are REACTIVE (This is rather poorly written on MM Pg. 61, but this is my interpretation) this means that instead of the single reaction that other combatants on the field are limited to, these creatures have a total of Seven reactions, one for each weapon and one for their tail.
Step 2) How do they Fight?
As Battle-Captain, the Marilith deploy their minions to occupy the enemy forces on the field, meanwhile, they will spend their time observing and identifying the threats on the battlefield. While their passive perception is quite low, this isn’t really an issue when you consider that they have true sight, if they choose to pay attention, they see it.
Having identified and chosen a target, the Marilith will allow its subordinates to continue to engage other combatants on the field while it utilizes its teleportation ability to immediately engage its one target. Like all burst attackers, the Marilith will attack spell-casters especially clerics first, then engage any ranged or stealthy types.
By telepathic command, the subordinate minions that were currently fighting the target will switch to the HELP action, granting the Marilith advantage on each of its attacks.
The Marilith will then attack the now isolated target beginning with its tail attack. Success with the Grapple is automatic, though it can be escaped with enough effort. Grappled targets are subject to the restrained condition.
The Marilith will continue its attacks on its single isolated target, bringing all six weapon attacks to bear. Thanks to the conditional modifiers, each of these attacks is made with advantage, further any counterattack against the Marilith will be made with disadvantage.
The Marilith utilizes this attack method because it enjoys seeing the terror in its victims’ eyes as it realizes that not only is it going to die, but there is also nothing it can do to change that fact.
A Special insult, if available, would be to teleport with the restrained victim and dangle them over some special danger, great height, pool of acid, whirling death blades.
Some Marilith are said to collect the “Death Screams” of their victims as an amusement.
Step 3) DM Tips and Observations
Once again, the AC of this creature is far to low. As a CR 16 creature, Tier 3 and four characters with average attacks will hit at least half of the time. I would increase the AC to 26.
Published Hit points for a Marilith are 189. As strong demons, they were created and will only survive if they have near physical perfection. In this case, drop the rolled Hit Points and Assign the 270, personally, I wouldn’t quibble about taking them to a nice round 300.
War and Strategy revolve around knowing your opponent and their previous battles, yet the Marilith is not proficient in any skill. At the least, they should be proficient in perception, history, arcana, and intimidation.
Consider this: The Marilith is effectively the demonic melee ‘champion’ and their race is undoubtedly “Savage”. Allowing the Marilith the Increased critical ability, i.e. a critical hit on a 19 or potentially a 18 or better would have a real impact. Additionally, when a critical hit is scored, allowing an additional 1d8 damage die…
It is exceptionally rare for a Marilith to be encountered as an isolated creature, they almost always have subordinate minions with them, if not demonic then whatever happens to be available will do.