Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
In this case going for all ap. I build my items in this order because I would expect by doing so the ap will be buffed by majis when you use your ult to snipe down low targets.
I get the sorcerers boots because it adds to his spell penetration in the case you see that you will be facing a group with not a lot of characters with slowing abilities get mercury treads. I then get archangel staff because ezreal needs the mana. Lich bane comes next so that your mystic shot starts doing a lot more damage. Then comes the void staff so if your enemies seem to take to much magic damage they will not anymore. Finishing with zonyas for immune and lots of ap.
I use ghost because you can chase targets past towers.
Always finish with ignite.
Make sure to spam with mystic shot to conserve mana and only do essence and arcane shift if you think you can get a kill or get them real low so they will go back and you can push or also go back. Also communicate with team mates to snipe people with ult.
Since Lichbane buffs mystic shot once you get it you will be able to harass even more by following this procedure. Essence flux when they are behind their minions regular attack arcane shift past their minions and mystic shot them then run back.
Make sure to not use this if you think they might be able to turn around and kill you. In this case do essence run at them while trying to attack, mystic shot and use arcane shift to port away or behind bushes.
Also if you need to chase people down pass there towers now is the time to do it. If you feel you don't need the magic penetration get rod of ages or the scepter
Try to always stay at the back of your group because your squishy but be ready and close enough to jump in and kill.
Lots of damage out put
Can snipe people from across the map
Will be able to harass people even if they are behind their minions
Mana needs to be conserved early game
Squishy the entire game
not able to harass as well as a hybrid or ad build.
Please comment any questions or concerns and rate please