Black and Tainted Ceisiwier

Familiar Camouflage. The Tainted has advantage on Dexterity (Stealth) checks made to hide in terrain that it considers familiar. It can by any terrain that it makes its layer or home in.

Enhanced Cunning. The Tainted has advantage on Intelligence, Wisdom, and Charisma saving throws against magic.

Amorphous. The Tainted can move through a space as narrow as 1 inch wide without squeezing. 

Innate Spellcasting. The Tainted’s innate spellcasting ability is Intelligence (spell save DC 14). He can innately cast the following spells, requiring no material components:

At will: nondetection (self only)

1/day each: blindness/deafness, blur, disguise self

Insanity. The Tainted has advantage on saving throws against being charmed or frightened.

Spellcasting. The Tainted is a 11th-level spellcaster. His spellcasting ability is Charisma (spell save DC 14, +6 to hit with spell attacks). The Tainted knows the following sorcerer spells:

Cantrips (at will): acid splash, light, mage hand, poison spray, prestidigitation

1st level (4 slots): false life, mage armor, ray of sickness, shield

2nd level (3 slots): crown of madness, misty step

3rd level (3 slots): gaseous form, stinking cloud

4th level (3 slots): blight, confusion

5th level (1 slot): cloudkill

6th level (1 slot): disintegrate

Acidic Tendril. As a bonus action, by using his speed, the Tainted can create an acidic tendril within 20 feet of himself. 

The tendril has AC 16, 1 hit point, and immunity to all conditions. If it has to make a saving throw, it uses the Tainted's saving throw bonus for the roll. It is the same size as the Tainted, and it occupies its space. On its turn, the Tainted can mentally command the tendril to move up to 20 feet in any direction (no action required). If the tendril is ever more than 20 feet from the Tainted at the end of his turn, it is destroyed. A 6 inch diameter tether of slime extends between the Tainted and the tendril, the tether is immune to all damage. 

• When the Tainted takes an Attack action on his turn, any attack he makes with that action can originate from your space or the tendril's space. The Tainted make this choice for each attack. Spells cannot originate from the tendril.
• When a creature that the Tainted can see within 5 feet of his tendril moves at least 5 feet away from it, you can use your reaction to make an opportunity attack against that creature as if you were in the other's space.

Multiattack. The Tainted makes two melee attacks.

Tendril Strike. Melee Weapon Attack: avg +4 to hit, reach 5 ft., one target. Hit: 9 (2d6+3) bludgeoning damage plus 3 (1d6) psychic damage.

Spear. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d8) piercing damage.

Change Shape. The Tainted magically transforms into an ooze, or back into his true form. He reverts to his true form if he dies. Any equipment he is wearing or carrying is absorbed by the new form. In ooze form, the Tainted retains his alignment, hit points, Hit Dice, and Intelligence, Wisdom, and Charisma scores, as well as this action. His statistics and capabilities are otherwise replaced by those of the new form.

Create Green Slime (Recharges after a Long Rest). The Tainted creates a patch of green slime. The slime appears on a section of wall, ceiling, or floor within 30 feet of the Tainted.

Tendril Shift. As a bonus action, the Tainted can teleport, magically swapping places with the tendril at a cost of 10 feet of his movement, regardless of the distance between himself and the tendril.

Tendril Retaliation. When a creature that the Tainted can see within 5 feet of his tendril moves at least 5 feet away from it, you can use your reaction to make an opportunity attack against that creature as if you were in the other's space. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 9 (2d6+3) bludgeoning damage plus 3 (1d6) psychic damage.