Ancient Radiant Dragon

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

It's a sunny day. Heals equal to radiant damage dealt to it.

Good bye. Can teleport to lair.(once a day)

Have a great day. (6d10) radiant damage every physical attack.

Don't look at me. Every four rounds hostile creatures who see the dragon have a chance go blind for (1d4) rounds (Wisdom saving throw DC 20)

Can't see me. Can turn invisible as an bonus action. Does not need spell slots.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws. For a Radiant dragon it can use its horns to toss a medium or small sized creature into air catch them in with a bite then, slam them to the ground. 

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 21 (2d12 + 10) piercing damage plus 14 (4d6) radiant damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 10) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d10 + 10) bludgeoning damage.

Horns. Melee Weapon Attack: +17 to hit, reach 18 ft., one target. Hit: 21 (2d12 + 10) bludgeoning damage.

Slam. add 3d8+10 (dex saving throw DC 16) 

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 21 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Radiant ram.  Rush Forward in a straight line (3d10+10) bludgeoning damage and 8d6+10 radiant damage (DC 17 dex save for half damage.) Does not stack with-Have a great day.

Radiant Breath (Recharge 5–6). The dragon exhales Radiant energy in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 91 (26d6) radiant damage on a failed save, or half as much damage on a successful one.

The dragon 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. The dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.