Flameskull

AC 13 - HP 40 - fly 40 ft. (hover)
Resistance Lightning, Necrotic, Piercing
Immunities Poisoned, Prone
Illumination; Magic Resistance; Rejuvenation
Multiattack. 2 attacks
Spell save DC 13, +5
Fire Ray: +5 (30) / 3d6 fire.
1 (3): Magic Missile, Shield
2 (2): Blur, Flaming Sphere
3 (1): Fireball