Nasus is a very powerfull champion in a skilled hand. This build allows you to become a battlefield master. You will be able to crowd control, lane managment and of course damage
dealing.

Runes and mastery tree are your own choice, but my preferences are Greater Quintessence of Fortitude x3 and defence masteries with dodge. This will save you in bad situations.

Summoner spells
I prefer Exaust and Flash or Ghost. You don't need Clarity, Clairvoyance, Revive and Smite. You cam also choose Ignite,Teleport and Cleanse. Heal and Fortify are optional skills.

Core Item Build

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You can buyif u have enough money andif u are playing carefully.

Early game:
Try to ger first blood on top or bottom using Spirit Fire and Siphoning Strike. You can
take SS first but in early ganks SF is good too.

Mid game:
Manage you lane and u can get many expearience and gold by wipeing out creep waves, so u will be level up and purchase items faster. SS is good in destroing towers and u can take them down quickly. Your ultimate and wither are very usefull in ganks and team fights. Try to use SS as last hit and kill enemy.

Last game:
With core item build you SS is extremely strong and your ult shines. You can take down all enemy team, even without team help. Kill them all!!!

Good luck and have fun, summoners! Tips and comments are welcome.