crystalized necrotic flame

you create a crystal that can be dropped anywhere. once dropped you can activate it from up to 120 feet away. once activated it will explode and anyone within a 10 foot radius must make a dex save of 16 or be paralyzed. then dark purple crystals grow around the ten foot radius and set on fire. the fire is a light blue color and anyone caught within its flame takes 1d6 fire damage, 1d8 necrotic damage and is now paralyzed. all necrotic damage you opponents take you heal. This spell last up to 20 turns.