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.
Nasus - Skills
As Nasus i just make sure to get my Q(Siphoning Strike) in level 5 so fast that i can.
Then my Wither and Spirit Fire.
Nasus - Summoner Spells
For summoner spells i use Teleport and Ghost.
Ghost: To get away as fast as i can, or just to gank(to get slow on fast!)
Teleport: I use teleport to gank(If i have wards behind or right at them, they cant see me cuz its in stealth) or just to get in lane fast to get XP.