The Xerath script is actually a bug being taked advantage of by using a script to get it perfect..

In a custom game i was able to replicate the bug without scripting by standing in the same spot he did and watched the live feed to get an approximate time you need to channel the q (like almost instantly but not...) and was able to hit everything 3 or 4 times out of 20 attempts so this is actually a bug on riots part.