I recommend this deck if you enjoy summoning a swarm of aggressive death effects in order to eventually hit your opponent with an absolutely massive unit. Play this if you enjoyed playing They Who Endure aggro.
Thresh Nasus is a very controlling midrange deck built around killing as many of the opponents units and your own units as possible in order to get a very large Nasus or to level your Thresh so you can pull out a very large Nasus. Once you have a massive Nasus you can finish the game off with a big Atrocity or you can just kill all of their Fearsome blockers. It is very important with this deck to remember that Nasus is able to grow during combat so you should always order him last and you should identify ways of getting surprise lethals using things like Glimpse Beyond. In mulligans, I recommend keeping Dunekeeper, Thresh, Vile Feast and Withering Wail vs aggro, and Preservarium, Thresh, and Dunkeeper vs slower Matchups.