Pennywise the Dancing Clown

Shapechanger. Pennywise can use ITs action to polymorph into a Small or Medium creature. ITs statistics, other than ITs size, are the same in each form.

Phantasmal Vision. Pennywise can cast phantasmal force at will. The phantasm is not restricted to the size of a 10-foot cube.

Selective Invisibility. Pennywise can use ITs action to become invisible. IT can choose any number of targets to be able to see IT or ITs phantasmal force.

Regeneration. Pennywise regains 20 hit points at the start of its turn if it has at least 1 hit point. If IT takes psychic damage, this trait doesn't function at the start of ITs next turn.

Innate Spellcasting. Pennywise can cast spells. Any damage caused by ITs spells is psychic damage, instead of the designated type. ITs spellcasting ability is Charisma, Spell Save DC 18, Spell Attack Bonus +10. ITs known spells are listed below.

Voracious Hunter. Pennywise has advantage on all Constitution saving throws to maintain concentration.

27 Years. Pennywise cannot be killed, unless by a wish spell. If brought to 0 hit points in another way, IT will hibernate for 27 years before returning.

Spell List: Pennywise has following  spells prepared: 

Cantrips (at will): [Friends], [Minor Illusion], [ Prestidigitation], [Thaumaturgy], [Vicious Mockery]
1st level (4 slots): [Charm Person], [Inflict Wounds], [Tasha's Hideous Laughter]

2nd level (3 slots): [Crown of Madness], [Enthrall], [Hold Person], [Levitate]

3rd level (3 slots): [Fear], [Hypnotic Pattern], [Vampiric Touch]

4th level (3 slots): [Compulsion], [Phantasmal Killer],  [Confusion]

5th level (2 slots): [Dream], [Geas]

Multiattack. Pennywise makes two attacks, only one of which can be a bite attack. Any spellcasting cannot be used as part of the multiattack.

Claw. Melee Weapon Attack: +7 to hit, reach 5ft., one target. Hit 5 (1d8 + 3) slashing damage. Instead of dealing damage, Pennywise can grapple the target (escape DC 19).

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit 6 (1d6 + 3) piercing damage plus 10 (3d6) psychic damage. The target's maximum hit points is reduced by half the psychic damage dealt.

Pennywise can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Pennywise regains spent legendary actions at the start of its turn.

Bite. (Costs 2 Actions). Pennywise makes one bite attack.

Claw. Pennywise makes one claw attack.

Move. Pennywise moves up to ITs speed without provoking opportunity attacks.

Teleport. Pennywise casts dimension door.