This is the conversion of the Intellect Devourer inhabited void dragon from Valley of the Brain Collectors. Because during the course of the adventure I handed Maukui’s Host stat block to the players to run for a combat I decided to rework him into a boss encounter. Here is the original straight-up conversion though.
Armor Class 18 (natural armor)
Hit Points 172 (1 5d12 + 75)
Speed 40ft., burrow 30ft., fly 80ft.
STR 23 (+6) DEX 10 (+0) CON 21 (+5)
INT 14 (+2) WIS 13 (+1) CHA 17 (+3)
Saving Throws Dex +5, Con +10, Wis +6, Cha +8
Skills History +7, Perception +11, Persuasion +8, Stealth +5
Damage Immunities cold
Senses blindsight 60ft., darkvision 120ft., passive Perception 21
Languages As Maukaui
Challenge 13 (10,000 XP)
Legendary Resistance (3/Day). If Maukui’s Host fails a saving throw, it can choose to succeed instead.
Multiattack. The dragon can use its Alien Presence. Maukui’s Host makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +11 to hit, reach,.5 ft., one target.
Hit: 17 (2d10 + 6) piercing damage plus obliterate (The target must succeed on a DC 18 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the creature finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.).
Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target.
Hit: 13 (2d6 + 6) slashing damage.
Tail. Melee Weapon Attack: + 11 to hit, reach 15 ft., one target.
Hit: 15 (2d8 + 6) bludgeoning damage.
Alien Presence. Each creature of the dragon’s choice that is within 120 feet of the dragon and aware of it must succeed on a DC 14 Wisdom saving throw or become dizzy and sickened (mechanically as poison status affect) for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the dragon’s Alien Presence for the next 24 hours.
Breath Weapons (Recharge 5-6). The dragon uses one of the following breath weapons.
Suffocating Breath. The dragon consumes the air of all breathing creatures in a 60-foot cone. Each creature in that area must succeed on a DC 18 Constitution saving throw or is incapacitated and suffocating. As long as it conscious, a creature can repeat the saving throw at the end of each of its turns, ending the effect on it on a success. The affect automatically ends after five rounds (on the sixth round)
Void Breath. The dragon exhales an icy blast in a 60-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 54 (12d8) cold damage on a failed save, or half as much damage on a successful one.
The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The dragon regains spent legendary actions at the start of its turn.
Detect. The dragon makes a Wisdom (Perception) check.
Tail Attack. The dragon makes a tail attack.
Void Gaze. (Costs 2 Actions). The void dragon can use its gaze to confuse its opponents. Each creature within 30 feet of the dragon must succeed on a DC 19 Wisdom saving throw or become confused as the spell.
If Maukui’s host is killed then Maukui emerges within five feet of the body.
Additionally Maukui’s Host gains shield as a reaction ability while inhabited: An invisible barrier of magical force appears and protects YOU. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from magic missile
This dragon’s ebony scales and horns are flecked with a substance that glows an eerie green. The folds of its wings reflect a starry sky.