Xerath the magus ascendant is tired of being prisoned, so he is back, and with all his rage, he will help your team win. this build is pure power, you can easily get an invicted legendary with this if you know your distances, hide in bushes or behind walls, and wait for enemies to come, farm a lot and push, xerath is a good farmer. this xerath is going to be strong and very powerful, from the very begining go mid and start pushing your apponent no too far, just let him know you are there so you can farm until level 6, when you reach level 6, the fun begins cause you will be now able to get your first kil easily, after that go to store, and purchase the items i mentioned in this guide, keep doing this after you kill someone, you should be lebel 18, while the others still 14 to 16. that gives you a lot of advantage, so use it, be careful don´t enter directly to the battle keep your distance, and use the combos i mentioned in the Legendary part below. recently i made a 9/0/3 in classic with this build, and i´m just starting with it, in large battles 5*5 you wanna be behind your teamates since xerath has a lot of range, you are the best turret killer in your team with this build, so go help your friends destroy the more turrets you can, ata the end while your friends are fighting with the enemy your focus is to destroy all the inhibitors and turrets in the enemy´s layne, so wait for your minions and start destroying. i´m sorry for my english i know its not the best but i´m mexican, and i´m learning. so this is a very agresive character if you know how to use it, this build is working for me a lot until now, so please try it, have fun with it and comment XD.
im gonna be uploading videos of xerath to my youtube account, take a look to them.Kichuchillo youtube channel

Farm
use locus of power and arcano pulse to deal damage to an entire line of minions, move back a little use arcano pulse again, and finally get the big minion with autoattack.
W+Q+Q

Legendary
in order to kill a champion wait until level 6 if you can, then use Locus of power when you have an enemy close to you, use Mage chains and instatly use arcano pulse, that will stun the enemy then use arcane barrage if you didn´t get the kill finally use arcano pulse again. this also works a lot for crowd control
W+E+Q+R+Q