Ritual

The reason why Vale only targeted the lower body with his Spell Dispersion was simple. 

It was because most of the spells or curses that his classmates had cast were targeted at the Creature's head and chest…

So if Vale used his Spell Dispersion in all of its body, he would be helping the Creature disperse the Curse Spells instead.

Unfortunately, his Spell Dispersion wasn't in a perfect realm yet so it affects a certain area instead of a certain spell in the area. 

He can disperse the spell that was cast even by his classmates.

With this problem, he had to learn how to adjust. Of course, this is only a temporary solution to this problem. He can permanently resolve this issue once he advanced his Spell Dispersion to level 7 or the early stage of the Advanced Realm. 

Well, that would still take a lot of time since it requires a huge amount of energy points.

He won't be able to collect that much any time soon.