Charged Lightning Explosion

This Spell has two phases, the charging phase and the explosive release phase. The longer the spell charges up, the stronger the release phase becomes. 

Charging Phase: Sparks start stricking towards your Body, channeling the electric energie around you in a big area. Within a 60 Feet radius, every creature that touches the ground has to make a constitution saving throw or be affected by the electricity beeing drawn towards the Caster. On a failed save they take 1d8 lightning damage and lose half their movement speed. On a success they take only half the damage and have no movement speed restrictions. Movement or actions of any other sort during this Turn by the Caster, disrupts the further charge of the Spell and terminates the Spell. Furthermore, disruption of the Casters concentration terminates the Spell as well.

Explosive Release: The Caster can choose to release all the build up Energie and create a powerful explosion around himself. Every Creature within a 30 Feet radius has to make an dexterity saving throw. On a fail it takes the whole damage while only taking half the damage on a success. The damage scales the longer it has been charged up starting at 10d8 with one charge and gaining 4d8 for every further charging phase. 

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the Damage in the charging Phase increases by 1d8 and on the explosive phase by 2d8. Furthermore, the charging adds 2d8 additional damage for each level above 5ths.