Belial, The pinnacle of mortal magic

Legendary resistance: 5/day. Belial can chose to succeed a saving throw that he has failed.

Belial is competent with light armor, he has advantage in constitution saving throws in  order to maintain concentration in spells. 

Change appearence: Belial can change his appearence using an action. He can choose the appearence of any humanoid creature that he has seen at least once in his life. He can maintain the appearence indifinitely. To discover that this is not his true appearence, the charachter needs to make a contested roll using perception/insight against Belial's deception. A carachter wit a passive perception of over 28 discovers Belial's disguise automatically. 

• Belial doesn't need somatic components (S) to cast spells.  

Spellcasting. Belial  is a 20-level spellcaster. Its spellcasting ability is charisma (spell save DC 25, +15 to hit with spell attacks). Belial has the  following Divine soul sorcerer spells prepared:

Cantrips (at will): Fire Bolt, Guidance, Light,  prestidigitation, word of radiance and sorcerous burst. 
1st level (6 slots): Cure wounds,  shield

2nd level: (5 slots): Hellish rebuke and spiritual weapon

3rd level: (5 slots): counterspell, fireball and sending

4th level: (4 slots): -

5th level: (4 slots): Scrying

6th level: ( 3 slots): chain lightning and desintegrate

7t level: (3 slots) : Crown of stars, divine word and conjure celestial

8th level:(2 slots):  Sunburst and Demiplane

9th level: (2 slots): Wish, Mass heal, power word kill

Belial has 20 sorcery points that recharge every day at dawn  and he can use them to use the following metamagic options. (He can use two of them per spell)

Distant spell: When you cast a spell with a range of at least 5 ft. you can spend 1 sorcery point to double its range. If it has a range of touch, you make the range of the spell be 30ft.

Extended spell: When you cast a spell with a duration of 1 minute or longer, you can spend 1 sorcery point to double its duration. If the spell has concentration, you have advantage on any saving throw made to maintain concentration

Quickened spell: When you cast a spell with a casting time of an action, you can spend 2 sorcery points to change the casting time to a bonus action for casting. You can't modify a spell this way if you've already cast a level 1`+ spell on the current turn, nor you can cast a level 1+ spell on the current turn after modifying a spell this way.

Subtle spell: Whenever you cast a spell, you can use a 1 sorcery point without any V or M components except material components that have a cost specified in the spell. (He has to use 1 sorcery point for each one)

Highly transmuted spell: When you cast a spell that does damage, you can spend 1 sorcery point to change the damage type into any existing damage type.

Multiattack. Belial Does two attacks with his scythe, or makes one attack with the scythe and casts a spell.

Scythe. Melee Weapon Attack: +14 to hit, reach 5 ft., 1 target. Hit: 16 (2d12 + 4) slashing  damage. Belial can add the effects of a spell on the attack, he has to spend sorcery points equal to the spells level with a minimum of 1. For example, he can use 1 sorcery point to add the damage effects of a cantrip like fire bolt, adding 4d10 to the damage.(He can only use this feature once per turn and this ability a caster can use counterspell to try to negate this feature of taking action)

Belial can use a bonus action to make two angel wings sprout on his back, giving him 50 feet flying speed

Belial can use a reaction to cast counterspell.

When an attack hits him, he can cast shield using a reaction. (He can't cast shield on himself multiple times in a single turn)

When a creature hostile to him leaves his range, he can use a reaction to automatically make an attack against them.

Belial has 6 legendary actions and he recharges all them at initiative count 0.

Consume spell (3 actions):  If Belial is the objective of a spell or is affected by a spell, he can choose to consume the magic of the spell. The spell's caster and belial roll a d20 and add their spellcasting modifier. The one with the highest number wins. If Belial wins, he consumes the magic of the spell, the spell doesn't take effect and Belial regains spell slots with a total value equal to the level of the spell that the  divided by 2. If the caster succeds, the level of the spell increases by 2.  

Fast spell  (Costs 2 Actions). Belial  casts one of the spells in his spell lists using a spell slot. Without having to use an action, bonus actions and material components that don't have a specified value.

Teleport and attack (Costs 2 Actions). Belial teleports up to 60 feet and attacks automatically with his scythe a chosen enemy. This action triggers attacks of opportunity.

Reduce damage (Costs 2 actions). Belial reduces the damage of an attack by half.

Reaction ( costs 1 action). Belial gains one reaction to use automatically. (This legendary action can be used in any moment)

Belial has 1 Mythic actions and he regains all of them at dawn. 

Unearthly recover (Costs 1 Actions). Belial regains HP equal to half his max HP.

 Sorcerous restoration ( Costs 1 action). Belial regains autamatically all his sorcery points

Godly sacrifice(1 action): Belial can use this feature to completely heal all creatures that he chooses. They regain all of their HP, and negative effects are automatically finished. Then, Belial instantly dies and not even a wish or a true ressurection spell can revive him.