World Ender

You burst into the visage of a large demonic version of yourself, sprouting hellish black wings from your back, and any weapon you are holding also shifts to a jagged, black and red version of itself. All enemies within 10’ of you must make a CONSTITUTION saving throw or be frightened for the duration (enemies can use their action to attempt to succeed the save on their turn). While in this altered form you are considered 1 size larger. For the duration any melee attacks you make with your altered weapon deals an additional 1d6 necrotic damage and heals you for that amount. Killing a creature while in this form extends the duration of the spell by 6 seconds for every creature slain.