Chimera King

Legendary Resistance (3/Day). If the Chimera King fails a saving throw, it can choose to succeed instead.

Pack Tactics. The Chimera King has advantage on an attack roll against a creature if at least one of the King's allies is within 5 ft. of the creature and the ally isn't incapacitated.

Keen Senses. The Chimera King has advantage on Wisdom (Perception) checks.

Infused exoskeleton. The Chimera King can't be affected or detected by Spells of 3rd level or lower unless it wishes to be. It has advantage on Saving Throws against all other Spells and magical Effects.

Adaptive Evolution. As a bonus action, the Chimera king can change his abilities, based on his needs. He has 4 options. 

Fighter. The King's form shifts into a sleeker build, putting an emphasis on speed and multi attacks. In this form, the Chimera King speed becomes 50ft can make three attacks per turn and during his turn, when he makes a melee attack against a creature, that creature can’t make opportunity attacks against him for the rest of your turn.

Caster. The King's form grows 2 tentacles with eyes at the ends from his back, the emphasis is on magic. In this form, the Chimera King can cast spells with a casting time of one action as a bonus action. While in caster form the king has immunity to magical Fire, Cold, Lightning damage.

The grown eyes can be used in place of an attack.

1. Paralyzing Ray. The targeted creature must succeed on a DC 16 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

2. Slowing Ray. The targeted creature must succeed on a DC 16 Dexterity saving throw. On a failed save, the target’s speed is halved for 1 minute. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Siege. The King's form grows greatly in size, becoming a large creature and gaining doubled damage against objects. His speed is reduced to 15ft, the bite attack now heals the King for the damage done. 

Travel. The King's form grows smaller retracting it's exo-skeleton, the king sprouts wings and gains a speed of 100ft.

Spellcasting. The Chimera Ant King is a 15th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). The Chimera Ant King has following Sorcerer spells prepared: 

Cantrips (at will): Acid Splash, Poison Spray, Light
1st level (6 slots): Jump, Sleep, Magic Missile, Detect Magic

2nd level (3 slots): Blindness/Deafness, Enhance Ability, Detect Thoughts, Web, Spider Climb, See Invisibility, Phantasmal Force, Misty Step

3rd level (3 slots): [ounterspell, Fly, Haste, Hypnotic Pattern, Water Walk

4th level (3 slots): Stoneskin, Polymorph, Confusion

5th level (3 slots): Dominate Person

6th level (2 slots): Circle of Death, True Seeing, Eyebite

Fighter Form.

Multiattack. The creature can make two bite or claw attacks and one tail swipe per round.

Bite. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit:  18 (4d6 + 8) Piercing damage. 

Tail Swipe. Melee Weapon Attack: +13 to hit, range 5 ft circle. Hit: 24 (3d10 + 8) Bludgeoning damage. When a creature takes damage from a Tail Swipe, the creature must make a DC15 Dexterity saving throw or be knocked prone.

Claw Strike. Melee Weapon Attack: +13 to hit, range 5 ft, 1 target, Hit:  18(4d6+8) Slashing damage. The target must succeed on a DC20 Acrobatics check or be grappled. 

Caster Form.

Spellcasting. The Chimera King can cast his innate spell, as an action and bonus action

Bite. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit:  18 (4d6 + 8) Piercing damage. 

Tail Swipe. Melee Weapon Attack: +13 to hit, range 5 ft circle. Hit: 24 (3d10 + 8) Bludgeoning damage. 

Claw Strike. Melee Weapon Attack: +13 to hit, range 5 ft, 1 target, Hit:  18(4d6+8) Slashing damage.

1. Paralyzing Ray (recharge 5-6). The targeted creature must succeed on a DC 18 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

2. Slowing Ray. (recharge 3-4). The targeted creature must succeed on a DC 18 Dexterity saving throw. On a failed save, the target’s speed is halved for 1 minute. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success

Siege Form.

Bite. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit:  32 (8d6 + 8) Piercing damage.  All damage dealt by a bite attack heals the king for the full amount.

Tail Swipe. Melee Weapon Attack: +13 to hit, range 5 ft circle. Hit: 38 (6d10 + 8) Bludgeoning damage. When a creature takes damage from a Tail Swipe, the creature must make a DC15 Dexterity saving throw or be knocked prone.

Claw Strike. Melee Weapon Attack: +13 to hit, range 5 ft, 1 target, Hit:  32(8d6+8) Slashing damage. The target must succeed on a DC25 Acrobatics check or be grappled. 

Travel Form.

Multiattack. While in Travel form the king can make two attacks per round.

Bite. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit:  18 (4d6 + 8) Piercing damage. 

Tail Swipe. Melee Weapon Attack: +13 to hit, range 10 ft line. Hit: 24 (3d10 + 8) Piercing damage. 

Claw Strike. Melee Weapon Attack: +13 to hit, range 5 ft, 1 target, Hit:  18(4d6+8) Slashing damage. 

Death Knells. Upon reaching less than 100 health the Chimera King lets out a screech. Creatures within 30ft must make a DC18 Constitution saving throw, on failure the creature is frightened of the Chimera King. On success, the creature is immune to the Death Knells for 24hours.

The Chimera King can take 3 legendary actions, using its attacks or spells. It can take only one legendary action at a time and only at the end of another creature's turn. The Chimera King regains spent legendary actions at the start of its turn.

Attack. (Costs 1 Action). The Chimera King makes one claw attack or tail attack.

Feed. (Costs 2 Actions).The Chimera King makes one bite attack. 

Evolve. (Costs 2 Actions). The Chimera King uses its Adaptive Evolution.  

Cast Spell. (Caster form, Costs 2 Actions). The Chimera King can cast a spell.