General Info
His affinity weapon is the judicator and his alt-form is the vhoscythe. Noxus is probably the trickiest hunter control-wise. His judicator bounces on walls and works well in tunnels and closed space because it keeps going until it hits a hunter escapes to the sky, or runs out. If Noxus charges it, he can freeze the other hunter in ice and make them vulnerable for 5 seconds. This allows time for at most 4 shots with the judicator.
Strategy
Noxus should attempt to freeze other players and headshot them, either with the Imperialist or 4 judicator shots. Remember to zoom if using the Imperialist. To headshot a character frozen while transforming into their Alt. form, shoot at where there head would usually be, not at where it is. Your shots will only hit if you aim at where they would be if they were standing still. Freezing easily disposes of Alt. forms as they need to close in to damage you.
Be careful not to chase with a charged judicator as they will run backwards while shooting at you. You will die very quickly.
When freezing Trace step behind him before he unfreezes or he will often headshot you with the Imperialist.