Nasus is a great Champion to use, with all his abilities helping out to dish damage or aid other Champions in battle. His Siphoning Strike is great if farmed correctly, and it'll do tons of damage if done so. His slow, Wither, now always reaches full potential through tenacity, and is one of the best, slowest slows in the game. His Spirit Fire, while still costing tons of mana, is great for scaring away enemy champions and allowing more damage output, and his ultimate is great for survivability, damage, initiation, and a lot of other things.

Pros:

A great tank with above average damage output.
Very good lane survivability due to his Life-Steal.
One of the best slows in the game.

Cons:

Needs good farming for proper damage output.
Consumes a lot of mana if careless.
No ranged attacks.
Fairly slow and easy to get away from.

Passive: Soul Eater

Nasus drains his foe's spiritual energy, giving him a natural 14/17/20% lifesteal. The lifesteal value increments at levels 1,6, and 11.

This ability was recently buffed in the early August patch. It used to give 10%/15%/20%, but now it's a little increased at the early levels. This is what allows Nasus to Jungle, without the use of Vampiric Scepter. It's also good for general sustainability.


Q: Siphoning Strike.

Nasus strikes his foe, dealing damage and increasing the power of his future Siphoning Strikes if he slays his target.
Nasus's next attack will deal 30/50/70/90/110 ( + ) physical damage. Siphoning Strike permanently gains 3 damage whenever it kills an enemy.

Cost 20/25/30/35/40 Mana
Range 300

This is what allows Nasus to deal his damage while still being a Tank. Every last hit minion or champion kill gives this ability a +3 damage bonus, so it's very important to farm this ability well.

W: Wither

Nasus ages his target, decelerating their movement and attack speeds over 5 seconds.

Nasus ages his target, slowing their movement and attack speed by 35% and reducing it further by 3/6/9/12/15% each second for 5 seconds.

Cost 80 Mana
Range 700

As I said in the introduction, this ability will now always reach it's maximum slow duration, making it just an awesome slow.

E: Spirit Fire

Nasus unleashes a delayed spirit flame at a location, dealing damage and reducing the armor of enemies who stand on it.
After a brief delay, the target area becomes desecrated for 5 seconds. Enemies in the area have their armor reduced by 20/25/30/35/40 and are dealt 20/34/48/62/76 (+0.2) magic damage each second.

Cost 70/85/100/115/130 Mana
Range 650

Recent patch fixes:

No longer has a 0.5 second delay before taking effect
Now deals half of its damage initially and the other half over the duration -- initial 55/95/135/175/215 (+0.6 ability power) Magic Damage and 11/19/27/35/43 (+0.12 ability power) Magic Damage each second for the next 5 seconds

This is the ability we initially use for jungling, because it deals initial damage and damage over time, while reducing armor so our basic attacks hit harder. It's also great for telling champions to stay away from our little circle of death.

R: Fury of the Sands

Nasus unleashes a mighty sandstorm that batters nearby enemies. While the storm rages, he gains additional Health and drains nearby enemies' max health and converts it into bonus damage for the duration of the skill.
Nasus becomes empowered in the sandstorm for 15 seconds, gaining 300/450/600 health. While the storm rages, he deals 3/4/5 (+0.01)% of nearby enemies' health each second (240 damage max per second) as magic damage and converts it into bonus attack damage.

Cost 150/150/150 Mana
Range 20

This is just a nice kind of scary ultimate. Nasus gets bonus health, and drains the health of nearby champions and adds it to his attack damage. It's great for initiation. Also, you don't have to build items that grant HP (Like frozen mallet) because of this HP increase.

Currently still working on the guide. But, any feedback would be awesome, since Nasus is a new Jungler.