Sources
CR
Type
Size
Alignment
Movement

Berlain Shadowdusk

Medium Aberration, Chaotic Evil

Armor Class 12, 15 with mage armor
Hit Points 99 (18d8 + 18)
Speed 30 ft.
STR
10
+0
DEX
14
+2
CON
12
+1
INT
20
+5
WIS
15
+2
CHA
16
+3
Saving Throws INT +9, WIS +6
Skills Arcana +13, History +13
Damage Resistances damage from spells; nonmagical bludgeoning, piercing, slashing, (from stoneskin)
Senses passive Perception 12
Languages Common, Deep Speech, Grell, Undercommon
Challenge 12 (8,400 XP)

Traits

Magic Resistance. Berlain has advantage on saving throws against spells and other magical effects.

Spellcasting

Spellcasting. Berlain is an 18th-level spellcaster. Her spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). Berlain can cast disguise self and invisibility at will and has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation, shocking grasp

1st level (4 slots): detect magic, identify, mage armor*, magic missile

2nd level (3 slots): detect thoughts, mirror image, misty step

3rd level (3 slots): counterspell, fly, lightning bolt

4th level (3 slots): polymorph, fire shield, stoneskin*

5th level (3 slots): cone of cold, scrying, wall of force

6th level (1 slot): globe of invulnerability

7th level (1 slot): teleport

8th level (1 slot): mind blank*

9th level (1 slot): time stop

*Berlain casts these spells on herself before combat.

Actions

Dagger. Melee or Ranged Weapon Attack: +6 to hit, reach 5 ft. or range 20/60 ft., one target. Hit:4 (1d4 + 2) piercing damage.

Bonus Actions

Fused Form. As a bonus action, Berlain can use her extra mouth and arms to cast any cantrip she has prepared.

Lore

A little over a year ago, Berlain and her brother Korva briefly entered the Far Realm, whereupon they became fused into a single physical form. This merging obliterated most of Korva's body and personality, leaving Berlain with an extra mouth and an extra set of arms that once belonged to her brother. She also inherited a few of his internal organs and personality traits. She can speak using one or both of her mouths.