I hardly ever play Xerath to clarify, but I din't late game he'd never have time to make use of Blackfire torch's dot since he's all about nuking people down asap before his positioning becomes bad. It seems like a strong item if you can get fed enough and use it for harassment in lane, but by the time you're that fed that early then a death cap would have better scaling and make you snowball harder.
Again though, I am not an avid Xerath player.

ALL THE MAGIC PENETRATION!

but yea.... The changes to how Mpen works for S3 will be in his favor. (% penetration applies before flat now). I will probably still get sorc boots + haunting guise first. I might go void staff before rabadons now, not sure.

I think we can all agree that Xerath is a champion that has fallen off the face of the Earth since more mobile, stronger, and more efficient AP Carries have been released.

Xeraths laning isnt the storngest, no. But the stun shouldnt really be used for anything more than prepping a gank. As Dannamoth says, poke them with Q. Then once you've poked them with Q, poke them some more. Then, once you've poked them out of lane, rofl as you get an xp and gold advantage.

OR

Poke, casually poke, not aggressively to scare them off. Maybe down to about half HP. Then start mingling in the middle of your creep wave, to make them a little on edge, but dont be aggressive. Then Q them once more just make sure their hp is manageable, and just as Q comes up again, BOOM! FLASH< IGNITE< E< Q< AUTO TO DEATH AAAAHHH FIRST BLOOD!

ahem... or something like that. It's ususally quite successful for me. Auto attack harass lvl 1-2, if done correctly, is still lane changing early game. And with Xerath its even more important due to his minimal kill potential pre 6.

Thats just my 2 cents anyhow.

Do you know if they're planning on nerfing his % pen numbers on W? I really hope not.

Xerath with the new penetration changes has the potential to be completely frightening. Near True damage to tanks wut?

No.. his problem is he doesn't have enough range.... o_o

I don't have trouble killing people in lane... In fact, it depends who you are vs mid, and you forget HIS INSANE LATEGAME. He gets all the farm and ALL the magic pen. He seriously melts the tankiest guys like rammus with his w up. His magic pen is so good, I write home about it.

I'd follow the path of current AP assassin's and rush a full magic pen build:
Boots 1--->Haunting--->Sorc--->Void Staff w/Mastery+Runes

If you follow the preferred Q>W>E level path, by level 13 anyone with less than 105 MR is taking true damage from your spells in Locus of Power. You can throw in a Chalice or Rabadon if the enemy is averaging about 80 MR, but Magic pen looks to be very favorable because your W and the changes

Remember that AP is Xerath's best friend, and the only item that doesn't give substantial AP is Athene's Unholy Grail, which I would still say is core because always being able to poke and have enough mana is a must. You still want to stay away from Abyssal and DFG, just because they force you to get up close, but the magic pen changes will make it not hurt as much. I'd say he's looking pretty good, at least compared to his current state

Still not happy about nerfing his ult through syncing the animation. I loved the PEW PEW PEW effect of his ult. Now when its pew....pew.....pew....not as fun. Plus, it's still really easy to dodge if they have any moderate amount of movespeed. Not as bad as when it was synced up wrong and took forever to land, but still slow.