The enigmatic creature known as Nasus came to the League from a faraway world, and served as part of a vast and learned desert empire. There he was a respected and enlightened individual, having been made the Keeper of the Great Library. However, he was also part of a race of animalistic creatures that served as the rulers and protectors of the people. Unfortunately, there were others of his kind that believed they were more than protectors. They were under the egotistical delusion that they had ascended to become gods. War on Nasus's world was never more than a breath away, as these deluded others sought to enslave the people and establish a totalitarian sovereignty. In the midst of a heated battle, just as Nasus was about to slay his treacherous brother Renekton, he was pulled through the cosmos to a summoning circle in Runeterra.

At first angered that he had been taken just as he was about to cripple the enemies of his people, Nasus' advanced intellect won out when he heard the pleas for mercy from the summoners. He learned that Runeterra was also filled with its own brand of injustice. This danger was no less threatening than what he had fought against at home, and champions were needed to protect the people of this world. Heeding the call, Nasus chose to take his place in the League of Legends, knowing that his brothers and sisters would carry on the fight back home. These days, he is the Curator of the Sands, feeling most at home in the crumbling ruins of the Shurima Desert. However, recent disturbing news has reached the Keeper's ears - rumors that perhaps his brother had not in fact been left behind. If this were the case, the destruction of Renekton would quickly become Nasus' main priority, before this world to faces the threats of his brother's forked-tongue and endless ambition.

"The Curator of the Sands, though contemplative, is not to be trifled with."

We'll analise all of nasus' kit from r to passive.
Ultimate (r)- Nasus gains 600 health and his attack and spell range is increased.
During this time nasus also drains 5% of enemies max hp per second and
converts 6.375% of the dmg done to bonus ad.
Nasus' ult is an anti tank that can give him free ad, meaning he has to
survive for the full duration. This is Nasus' inherent tankiness.
Spell (e) - Nasus creates a circle that deals dmg and reduces the enemy's armor by
20-40.
This is what makes him so strong early game unlike what most people think
Spell (w) - This spell slows an enemy champion and lowers their attack speed. This
is what gives nasus the ability to gank and to be an anti-ad. 95% is a
lot and this basically ensures that any gank will suceed as long as you
have enough dmg and he isn't super fed.
Spell (q) - This spell is where most of Nasus' dmg comes from. As much as it does
have all its potential riding on stacks. Even if it isn't stcked it
still is very strong (Nasus non-stacked q =110, ezreal q=115).
Passive - This is what gives Nasus an advantage in dueling and what gives his
lane dominance early game by having the most sustain. The only champs
that can outsustain him are Nunu, Vlad, Xin Zhao, Aatrox and Chogath.

Nasus is one of the most flexible champions, you can build anything on him and get away with it. I'll show you what runes I'd normally take on nasus.

Reds: Armor pen, Hybrid pen, AD (helps you cs and bypass armor early on)
Yellows: Hp, Percentage hp, Armor (Yellows must be used for def)
Blue: Mr, Mr scaling, CD, Ap (Lots of options)
Quints: Armor,Mr,Hp,Lifesteal,Percentage Hp,Armor pen, Hybrid pen

I prefer to run a 21-2-7 mastery page on masteries though it is erfectly normal to run 21-9/9-21/0-21-9. I just like my setup because I get bonus armor and Mr while still getting dmg and MS.

Viable options for nasus

Heal: It heals (Duh) but the most important bit is to use it b4 u ult because it will
give you a bonus to your lifesteal.
Ghost:Gives you more chasing power and makes it easy to get away from any situation.
Teleport: Gets you back to lane quickly so that you don't miss Cs (I generally don't
Back until I can get my 1st item or I'm near dead and out of pots.)
Barrier: Its a shield, its more tankiness
Flash: Always useful
Exhaust: Gives you protection early game and gives you a second W
Ignite: Who can't take ignite?

Pros Cons
Infinite source of dmg People know he is a force to be reckoned with and camp
Lots of sustain No spells that buff himself
Great duelist (armor reduction) Has to ignore the enemies early game while farming
One of the fastest pushers Kited like mad
Can solo Nexus turrets

Nasus Needs Teamwork??????? All he does is charge in and tank all their dmg while walking to their carries, q adn they're dead lol.

The most important skill for Nasus is IGNORANCE, during the laning phase you will ignore the enemy and just cs. Mid game you ignore your whole team's pinging, just keep pushing, getting stacks, bugging their whole team by applying pressure and forcing them to retreat to defend. Late game you just ignore the world. If your team needs help coz they r losing like mad then yeh of course help them, if not you just walk into their base and laugh while soloing their turrets, q-ing minions to recover hp and then taking out the next set. Just remember, until either you take the inhib in your lane or the enemies get to your inhib turret, you stay top and farm.