Dark Aura. Any creature allied with Yveltal can add one extra dice roll to attacks that are purely psychic.

Multi-attack. Yveltal makes 3 attacks, 2 with claws and knees with tail

Claw. Melee Weapon Attack: +8 to hit, reach 10 ft., 1 target. Hit: 8 (2d8 + 4) [slashing] damage. 

Tail. Melee Weapon Attack: +8 to hit,  reach 10 ft. ,1 target. Hit 8 (2d8 + 4)

Dark pulse. Dark psychic powers twist reality on a shockwave the pulses out from the origin to everything around it. Deals 10 psychic damage to everyone except the user. 

Taunt. Yveltal chooses a target to taunt. This target must make a DC:15 wisdom saving throw at the start of each of its turns. On fail, the target may only perform damaging moves targetting Yveltal. This stays in effect until the target makes a successful saving throw. 

Sucker Punch. Yveltal withholds it's action until an enemy makes an attack against it. It can then choose to make  Single melee attack. On a hit, the target is unable to complete it's attack and their turn is skipped. 

Oblivion wing (1/1). 

Yveltal takes to the sky, unleashing a deadly beam of chaotic energy. Everyone within 40ft of the blast makes a DC:15 dexterity saving throw, taking half damage on success and full damage on fail. 3d8 psychic damage.