Legendary!

"Boom!"

After the fusion of the Thunder-type spell and the Fire-type spell, its power increased manyfold and exploded with a massive bang. The intensity of its attack was so strong that even Merlin was almost unable to withstand it. His Enervating Halo held up for a second but shattered in the next instant. The powerful attack even caused Merlin's body to be blown away violently and smashed against the wall.

One of the reasons was that the chamber was too small, therefore, the explosion of the spell affected Merlin as well. This helped Merlin discover how powerful his fused spell was. If even Enervating Halo was not able to withstand it, then it must have exceeded the Seventh-level and had achieved the Eighth-level.

"Not bad, really not bad, you've managed to perform a spell fusion. Though the fusion is only at the most elementary level, it's already admirable."