Running a 5e conversion of the 2nd edition adventure “A Darkness Gathering” – a campaign I have just called Thoughts of Darkness (heavily inspired by Bloodborne).  Its tuned to level 14 characters and my party is made up of 6 to 8 PCs.  A creature inspired by the Winter Lantern in Bloodborne and the grell philosopher from 4e. Another sewer native that would drop from the roof in ambush.  Its only CR3 so there should be at least 1 per PC to be any threat with overlapping auras.

Medium aberration, neutral evil
Armor Class 12
Hit Points 90 (10d8 + 10)
Speed 10 ft., fly 30 ft. (hover)

15 (+2) 14 (+2) 13 (+1) 12 (+1) 11 (+0) 9 (-1)

Skills Perception +4, Stealth +6
Damage Immunities Lightning
Condition Immunities BlindedProne
Senses Blindsight 60 ft. (blind beyond this radius), Passive Perception 14
Languages Grell, telepathy 60 ft.
Challenge 3 (700 XP)

Aura: Strange Song. All creatures within telepathic range of the winter lantern hear a strange song echo in their minds. At the start of the winter lantern’s turn, each creature within 60 feet of it must make a DC 15 Intelligence check or take 14 (3d8 + 1) psychic damage from this effect. If they can see the winter lantern this save is made with disadvantage and the Sanity ability score is used instead. On a success, they take half damage. A surprised creature has disadvantage on the saving throw and a grappled creature automatically fails this saving throw.

Multiattack. The winter lantern makes two attacks: one with its tentacles and one with its beak.  It may also use lightning lance or venomous mind if available.

Tentacle Rake. Melee Weapon Attack: +4 to hit, reach 10 ft., one creature.
Hit: 11 (2d8 + 2) piercing damage, and the target must succeed on a DC 11 Constitution saving throw or be poisoned for 1 minute. The poisoned target is paralyzed, and it can repeat the saving throw at the end of each of its turns, ending the effect on a success.

The target is also grappled (escape DC 15). If the target is Medium or smaller, it is also restrained until this grapple ends. While grappling the target, the winter lantern has advantage on attack rolls against it and can’t use this attack against other targets. When the winter lantern moves, any Medium or smaller target it is grappling moves with it.

Beak. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature.
Hit: 7 (2d4 + 2) piercing damage.

Lightning Lance (Recharge 1-2).The winter lantern discharges a stroke of lightning in a 50-foot line that is 1 foot wide. Any creature in that line must make a DC 12 Dexterity saving throw or take16 (3d6 + 6) lightning damage, and the target is blinded (save ends).

Venomous Mind (Recharge 5-6).The winter lantern releases a psychic bomb in a 15-foot sphere centered on itself. Non-aberrations in the area must make a DC 11 Intelligence saving throw or take 14 (2d8 + 5) psychic damage, and the target must make and choose a random target for its next attack action (save ends).

Appearing as a grell with an oversized brain covered in eyes the winter lantern is a dangerous foe that attacks from ambush similar​ to its smaller cousin.  It will use its song to lure creatures to it and generally sings right before it strikes.