New dark spell and a new defense
You could create two black spells and a new defense.
1. Rain Spell: the defense loses damage reached capacity. I suggest increase efficiency in Hell Tower and release the spell to TH10.
2. Spell of fire: damage the defenses continuously. Equal to the poison spell. I suggest increasing efficiency against the new defense will suggest and unlock in TH11
3. Whip water: triggers a rotating water jet, ie, turning on its axis.
These are my suggestions. I believe that might appeal to many clashers