AP Top Nasus is the best pusher, team fighter, farmer, and harasser in game. Before you rage on this guide you should read it and test it out at least once. Every queue I enter people will rage and say, "WTF, AP Nasus.... you troll...." Post game they seem to forget those words. All I'm saying is read it and try it out before you rate it.

Ps... if you dont want to deal with the rage just call top nasus and wait till you are destroying lane to announce ap or maybe not at all

Pros

Farming
Great early game harass
Unparalled team fighter
Pushes towers hard
Strong early/late game

Cons

Goes oom often early game
People will rage pregame(unless you dont tell them AP)
Very item dependant
Weak mid game

The flat AP increases your early game harass significantly and the flat mana regen allows for more often use of spells.

Magic Pen. can also be used but this will cut down on the early game damage which is used to shut down the opposing AP mid.

Pretty basic for an AP mid... maximize magic pen, CDR, and mana regen.

Flash/ Teleport.
Flash gives you the only escape you will have. Save this for those sticky situations.
Teleport keeps you in lane farming and harassing. It is also very useful if you keep an eye on your minimap. I have gotten many kills by using tele to drop in behind an enemy that is overextended in a lane or towerdiving a teamate.
Ignite I have been taking this lately becuase it is easy to land a Spirit Fire Ignite combo under their turret to finish off a kill from range.

The items are all chosen for their impact on teamfights.

Boots, 2 Health Potion and 2 Mana Potion are initial items because they allow you to dodge some or most harassment and improve last hitting and keep you in lane until you can afford the catalyst.

Catalyst the Protector is the first choice because it regenerates hp and mana in lane which will keep you farming and harassing.

Giant's Belt is second because even as ap nasus you will be in the middle of every single team fight and in order to be effective, you must be alive.

Mercury's Treads should be finished out for the increased speed and tenacity. Sorcerer's Shoes could also be substituted for more damage.

Rod of Ages and Rylai's Crystal Scepter are next. I usualy go with Rod of Ages first to get the extra hp and ap faster but finishing Rylai's Crystal Scepter first might prove more helpful. Rylai's Crystal Scepter is necessary because it adds an aoe slow to both your Spirit Fire and Fury of the Sands. Seeing as you will be in the middle of every team fight, this slow should be affecting every person on the enemy team. This allows you to hold them longer in one place making it harder for the other team to get to your adc. It also works just to maximize the effect of both of these spells keeping them in the area longer.

Chain Vest and Negatron Cloak are next to make you even tankier so that you will last even longer and do more damage. Pick whichever one first that will be most effective. Armor if the enemy ADC is fed or MR if the AP is fed. I almost always get Armor first because you should have been harassing their mid so hard they wont be doing much at this point.
Finish the Armor and MR off with a Frozen Heart and Abyssal Mask. Again, pick the one that will negate the most damage recieved so that you can last longer and deal more damage with that ult.

The final item can be very flexible. I usually go with a Guardian Angel because even though I'm tanky I still get focused and this allows you to respawn and finish them off. Liandry's Torment is another great item which adds another 4% per second to the ult damage. Other final items could be a Will of the Ancients or Hextech Gunblade. The will of ancients is cheaper and provides another team buff for fights but both provide a 20% spell vamp which results in a lot of HP if your ult is hitting 4 or 5 people for 7%/second.

This is how my build differs from pretty much every other nasus you have ever seen.



Soul Eater
(Innate): Nasus drains his foe's spiritual energy, giving him a natural 14 / 17 / 20% lifesteal.

Soul Eater is Nasus early game sustain. Auto attacks regenerate hp.


Siphoning Strike
(Active): Nasus next attack within 10 seconds will deal additional damage. Siphoning Strike permanently gains 3 stacked damage whenever it kills an enemy champion, minion or neutral monster.
Cost: 20 / 25 / 30 / 35 / 40 mana
Cooldown: 8 / 7 / 6 / 5 / 4 seconds
Physical Damage: 30 / 50 / 70 / 90 / 110 (+1.0 per attack damage) (+3 per enemy killed by Siphoning Strike)

Siphoning Strike relies on your ability to kill minions(or champions).

While I try to last hit with this as often as possible, the emphasis i put on this is minimal. This build does nothing to maximize the damage from this ability and instead focuses on nasus other multi-target abilities. That being said it can still do a fair amount of damage so by all means farm it when possible.

Wither
(Active): Nasus ages his target, slowing their movement and attack speed by 35%. Additionally, they are reduced further to reach an extra slow at the end of 5 seconds. If the duration of the slow is reduced, the extra slow will be applied faster for it to reach its maximum at the end of the duration.
Cost: 80 mana
Extra Slow: 12 / 24 / 36 / 48 / 60%
Cooldown: 15 / 14 / 13 / 12 / 11 seconds

I level up Wither third but max it second because it is very beneficial for completely shutting down the enemy AD Carry. A ranged ad with a 95% slow on attack speed is not someone to be scared of. It also is very useful for setting up ganks as it will root the AP mid in place and give your jungle plenty of time to run out and hit em hard.



Spirit Fire
(Active): Nasus unleashes a spirit flame at a location for 5 seconds. Enemies caught in the area are dealt a burst of magic damage. Additionally, enemies in the area are dealt magic damage each second and have their armor reduced while on there and for 1 extra second.
Cooldown: 12 seconds
Range to Center of AoE: 650
Radius of AoE: 400
Cost: 70 / 85 / 100 / 115 / 130 mana
Initial Magic Damage: 55 / 95 / 135 / 175 / 215 (+0.6 per ability power)
Magic Damage Per Second: 11 / 19 / 27 / 35 / 43 (+0.12 per ability power)
Total Magic Damage: 110 / 190 / 270 / 350 / 430 (+1.2 per ability power)
Armor Reduction: 20 / 25 / 30 / 35 / 40

Spirit Fire is my main source of farm, harass, and damage in a team fight. Lvl this up first and max it first because it puts the enemy AP in a world of hurt and makes them pay for every cs they get. Its aoe is large enough that you should be able to land it every time you cast and still have it hitting the minions for farming as well. In team fights this will deal large amounts of damage to everyone. It will proc Rylai's Crystal Scepter and slow anyone that inside the area. It will also drop everyones armor by 40. This causes your AD Carry's dps to increase very drastically. A single spell that does decent aoe damage, slows, and does an armor reduction. Try to tell me thats not op.

Edit: I just noticed I didnt comment on this... At Spirit Fire lvl 3 it should be dropping entire creep waves. Use this to push the minions under the enemy tower and deny cs to their mid. This results in most mana dependant mids to have to cast spells or drop behind in cs. They will then either get low mana or have to b and lose the xp.



Fury of the Sands
(Active): Nasus becomes empowered in the sandstorm for 15 seconds, gaining extra health. While the storm rages, he drains a percentage of nearby enemies max health each second (max of 240 magic damage per second per enemy) and converts 6.375% of the damage done into bonus attack damage for himself until the sandstorm wears off.
Cost: 150 mana
Cooldown: 120 seconds
Radius of AoE: 350
Health Gained: 300 / 450 / 600
Max Health to Magic Damage Ratio Per Second: 3 / 4 / 5% (+0.01 per ability power)
Total Max Health to Magic Damage Ratio: 45 / 60 / 75% (+0.15 per ability power)
Total Magic Damage Possible (to a single enemy): 3600
Total Bonus Attack Damage Possible (from a single enemy): 229.5

Fury of the Sands also applies the aoe slow from Rylai's Crystal Scepter. This means that they are fairly stuck to you as their hp drains steadily. If they focus you, you have built pretty tanky so they will be focusing for quite a while and will not be hitting your AD carry who will be able to pick them off 1 by 1. If they don't focus you, you will be slowing them meaning that it will take forever for them to get to your carry who can just kite them as your % drain takes its toll.

Your team effect with this build cannot be measured. Your wither will shut down the enemy AD Carry fairly effectively. Your Spirit Fire will deal decent damage, slow the enemy, and reduce their armor making your AD Carry more effective. Your Fury of the Sands will drain over 7% max hp per second of every person on the other team that comes within range. It will also apply a slow. The Abyssal Mask reduces their magic resist making any abilities your team uses more effective. Your Frozen Heart will further reduce the damage that any AD on the other team is dealing. If the other team doesn't focus you they will have to deal with all of these buffs to your team and nerfs to theirs. If they do focus you then you are pretty tanky which means that your teamates are free do dish out the damage. No other AP mid has this large of an effect on team fights.
Side Note: your jungle should be a dps or bruiser at the least. You will be soaking significant damage and do not need to have a tank top and jungle... make sure your teamates can take advantage of your dps boost and being focused and spend that time ripping through their carries.
AND REMEMBER TO ALWAYS BE WARDING... TAKE A TOWER AND WARD THEIR ENTIRE UPPER JUNGLE SO YOU CAN KEEP PUSHING.

Master Yi

Alpha Strike will cause all of your Spirit Fire to miss.

Meditate will negate any damage you manage to lane with Spirit Fire.

Highlander makes your Wither ineffective in ganks.

That being said, you can still keep even in cs and even push the turret hard when Yi backs. Your focus should be on ganking top and bottom lanes more so than trying to counter Yi.

Harass hard early landing Spirit Fire as often as possible. Farm up using Spirit Fire to drop entire waves of creeps with 1 spell. When the mid has to b for health because you have been harassing you should take complete advantage. Either hit the tower as hard as you can or run to another lane and put in a good gank. Make sure to buy wards when you b so that you will be more safe while pushing. 75g that saves your life even once will result in you getting much more gold from farm than if you had died. Be careful mid game as you don't have the completed items yet to really shine in a team fight. Late game when nearly full built you should be initiating and devastating the enemy team.

I know that this build will not make much sense until you try it. Most people have never seen it and dont really understand how big of an effect it truly has. Try it out. Please don't judge until you have made it to late game with this build.

That being said, this is my first guide. You have obviously noticed by now that I really didnt want to spend the time figuring out how to link all the pictures and ability effects. Constructive criticism is welcome.

P.S. I did not want to post all of the different champs and how this build should be played against them. If you think of a champion you believe this build would not work against comment on it. I will create a section that adresses these concerns.