Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
The purpose of this build is to maintain a ballanced DPS / tank nasus that can either deffend your base like no other or push against your opponents in a decent fashion.
This build is HIGHLY flexible. Many of the items can be switched out for other items depending on your preferences.
Early game relies on the DPS function of nasus. Don't attack enemies too often unless you know you can kill them. You're main goal is to vamp off of as many minions as you can before lvl 10 as I find that's when battles start to go beyond lane play.
Mid game switches from DPS to tank to keep you alive. This gets really helpfull as now you can take the fight to champions like Cho'gath who often have an entire mountain of health at their disposal.
Late game you should have you're own stacked bar of health and a fairly fast attack speed. You can easily take out turrets and can squish about any average character that comes at you. Guardian angel becomes really optional at about this time as death becomes inevitable. You can switch this out for any other tank item because it doesn't really help your health out.