My players scouted this room out and the geist and haunts didn’t see them but the character, Sylvanus, was appropriately freaked out by catching glimpses of shadowy figures moving around and something brushing past her that she beat a hasty retreat. The haunts I had function as trap that worked as an AOE and more powerful version of phantasmal killer.
MEDICAL CENTRE GEIST
Medium undead, chaotic evil
Armour Class 15
Hit Points 145 (17d8 + 68)
Speed 0 ft., fly 60 ft. (hover)
STR 6 (-2) DEX 20 (+5) CON 17 (+4)
INT 15 (+2) WIS 15 (+2) CHA 21 (+5)
Damage Resistances acid, cold, fire, lightning, thunder; bludgeoning, piercing, and slashing from non magical weapons that aren’t silvered
Damage Immunities necrotic, poison
Condition Immunities charmed, exhaustion, grappled, paralyzed, petrified, poisoned, prone, restrained
Senses darkvision 60ft., passive Perception 12
Challenge 10 (5,900 XP)
Incorporeal Movement. The geist can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.
Sunlight Sensitivity. While in sunlight, the geist has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.
Life Drain. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature.
Hit: 21 (4d8 + 3) necrotic damage. The target must succeed on a DC 17 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.
Terrifying Laugh. A geist can unleash a terrifying laugh as an action. The laughter lasts until the beginning of the geist’s next turn. All creatures within 30 feet of the geist when it begins to laugh, as well as all creatures that end their turn within that radius, must succeed at a DC 17 Wisdom saving throw, taking 56 (16d6) psychic damage on a failed save, or half as much damage on a successful one and becomes feared. The save is required only once per laugh. Those who succeed at their saving throws need not save against the same geist’s terrifying laughter for 24 hours.
Master of Haunts. Geists have the ability to take control of haunts. When a geist enters a haunt’s area of effect, the geist can immediately attempt to take over the haunt by making a Charisma check. If the result of the Charisma check is equal to or greater than the haunt’s CR, the geist takes over the haunt and maintains control as long as the geist remains within 1 mile. If the geist’s attempt to take control of a haunt fails, the geist must retreat from the haunt’s area of effect and cannot attempt to take control of the haunt again for 24 hours. When a geist controls a haunt, it can activate or suppress the haunt’s effects as a free action and the haunt automatically resets in half its normal time. A haunt under a geist’s control can still be neutralized when reduced to 0 hit points, but it cannot be permanently put to rest until the geist that controls it is destroyed. A geist can control a number of haunts up to its Charisma modifier at one time (usually five).
This disembodied phantom wears a a nurse’s outfit that swirl around a maw of sharp teeth.