Blade of the Necrotic

When this cantrip is cast a glowing translucent purple blade is formed above the forearm. This can be used as a melee weapon, and deals 1d8 Necrotic damage (2d8 at level 5, 3d8 at level 10, and 4d8 at level 16) + your spellcasting ability modifier. This blade will remain for 15 minutes, and once the time is up it'll vanish in a purple haze.