Brilliant Ethereal is a spell made on accident by Typhon Pureheart, a member of the Utopian Halo Dark Guild, when he held to much magic energy in one spot for to long, which eventually became a common used spell.
What Brilliant Ethereal does is it condenses ones Magic power into a ball of pure golden energy. It bends shadows towards the lights and pulls stray rocks and debris up to it. After waiting a minute or 2, a magic circle appears and the orb launches towards the opponent. This has the force to match that of Exploding Flame Blade in terms of raw power and can supposedly puncture through a mountain. Also, multiple other variations have been made to further enhance the spell.
There are multiple others who have copied this technique such as Lucy Heartfillia, Carla, Zyfe Hiyren, Typhon Pureheart, Death Ertim, and even Tristen Fett.