Nice but you've created a monster with abilities, reisstances & traits far beyond what a CR5 monster should have. I see you've sheared down Hit Points significantly in an attempt to balance but there are CR: 10 monsters who don't have that comprehensive a list of resistances & immunities. Turn resistance on a CR 5? Even true vampires don't have that. Sure you put in a way to shut down its most powerful abilities (like instant- unsavable death in 1d4+1 rounds) but they require a precious 3rd level spell slot. Beyond that there IS no 'remove disease' spell, that's wrapped up into Lesser Restoration.
This would be a great foe if it were CR: 10+ and a mid-campaign BBEG but it isn't, it's a very common enemy in the adventure path.
At CR 5 this should be severely trimmed back in my mind. A party of level 2 or 3 characters who encountered this wouldn't stand a chance in hell. IMHO Kyuss Spawn is best as a template that applies one or two of these traits while having powerful versions and less powerful versions of each.
They'll be bumping it at 5th level (and I grant them an extra feat at 1st level). There are 4 of them (Swashbuckler, Moon Druid, Bear Barbarian, Evoker Wizard).
I upped it to CR 7, but decreased its PB to +3, and slightly increased the damage of its attacks. Silver weapons now harm it, and it's DC's are reduced. Turn resistance was nixed.
Spawn of Kyuss
Medium undead, chaotic evil
Armor Class 15 (natural armor)
Hit Points 85 (13d8 + 26)
Speed 30 ft.
STR DEX CON INT WIS CHA
18 (+4) 9 (-1) 14 (+2) 6 (-2) 11 (+0) 15 (+2)
Saving Throws Con +5, Wis +3
Skills Perception +3, Stealth +2
Damage Resistances: bludgeoning, piercing, and slashing from nonmagical weapons that arent silver
Damage Immunities poison, necrotic
Condition Immunities charmed, frightened, paralyzed, poisoned, stunned
Senses Darkvision 60 ft., passive Perception 13
Languages Common
Challenge 7 (2,900XP)
Regeneration. The spawn regains 10 hit points at the start of its turn if it has at least 1 hit point. If the spawn takes radiant damage, this trait doesn’t function at the start of the spawn’s next turn.
Create Spawn. If a spawn hits a living creature with a Slam attack or Kyuss Worm attack, it transfers a Kyuss Worm to the creature. The creature must make a DC 13 Con save. On a failure the creature gains the poisoned condition as the worm burrows into its flesh, making its way toward the brain. This causes 1d6 points of necrotic damage at the start of each of the creatures turns until it reaches the brain 1d4+1 rounds later. When inside a victim, the worm can only be destroyed by remove curse, dispel evil, or greater restoration. Lesser restoration delays the worms progress for 24 hours, halting any continuing damage, but not removing the poisoned condition. These spells all affect multiple worms within the same victim. Worms cannot survive outside of a host for more than 1 round. A DC 15 Wisdom (Medicine) check also extracts the worm and kills it.
Once the worm reaches the victim’s brain, it reduces the targets HP to zero. A creature infected with a Kyuss worm automatically fails death saving throws. If the host dies it rises as a spawn of Kyuss 1d6+4 rounds later. Small, Medium, and Large creatures become spawn as described above; smaller creatures quickly putrefy rather than becoming spawn; larger creatures become normal zombies. Spawn (and spawned zombies) are not under the control of their parent but usually follow after whatever spawn created them.
Any creature that touches a spawn with an unarmed strike or other natural weapon is immediately attacked by a worm and must make the same saving throw.
Actions
Multiattack: The spawn uses its Horrifying Visage and then makes one attack: either a Slam attack or a Kyuss Worm attack.
Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage plus 14 (4d6) necrotic damage. If the target is a living creature, a Kyuss worm is transferred to the creature.
Kyuss Worm. Ranged Weapon Attack: +7 to hit, range 30 ft, one target. Hit: A Kyuss worm is transferred to the target.
Horrifying Visage. Each non-undead creature within 40 feet of the spawn that can see it must succeed on a DC 13 Wisdom saving throw or be frightened for 1 minute. A frightened target can repeat the saving throw at the end of each of its turns, ending the frightened condition on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to this spawn's Horrifying Visage for the next 24 hours.