Valance's mage ender

A spell created by a mage to kill other mages. This spell gathers immense energy from within you, and cripples the target of the attack.

Choose a target you can see in range, and make a ranged spell attack. On a hit, the target suffers 9d8 force damage, and cannot cast spells until the end of your next turn. If you hit them with this spell again on your next turn, this effect will stack and they cannot cast until the end of your next turn. 

Valance knows that a major weakness of spellcasters is close combat, so he adjusted this spell to also have a range of touch. Casting it on an adjacent target doesn't allow you to get the full power of the spell out, and will only deal 9d6 damage, but will still cause the target to be unable to cast spells as described above. Adjacent targets do not impose disadvantage on this attack if you cast it in this way. 

For every level above 7th this is cast, the damage increase by 1dx, where x is the value of the original attack (d8 for ranged, d6 for touch)