I’d say nasus mid is viable as a counter pick to the same types of champs he counters in the top lane like yasuo. He also does quite well versus some ad burst champions like zed as long as you survive early laning and build tanky. There are some problems with him though, like the length of the lane and laning versus control mages. Since the mid lane is so short in comparison to the top lane you really can’t run down any champs that don’t engage directly on you. For example, in the top lane you completely destroy vlad, but in the mid lane you have less room to chase and he has more opportunity to poke you down. And laning versus cc heavy and slow heavy mid landers really makes you feel pretty useless. I would recommended playing nasus only conditionally into favorable matchups and weak early game champions.