He has special eyes that can analyze any magic he sees and copy it for his own use and/or mess with others' casts of it as he sees fit. (Usually it's more or less instant, but there is some super super complicated stuff that takes longer to analyze, but that's kind of a tangent.) At this point in his canon, he can't analyze anything godly or anything, and it has to be magic-based specifically, but.

It's kind of like the Sharingan, except magic instead of ninjas.

(Also it sometimes causes him to go insane but you know what in the unlikely event that Alpha happens he'd probably pass out immediately from power overload...)