After buying "Touch of Nuru" and unlocking the starter you will be able to build this deck, do not go and buy it on the black market!
This decay deck is miles better than the 4000g one from last time, with witch doctors and necrogeddons included, as well as all the late game humans it can fit. Protect your harvesters, center units around rot eater and witch doctor, and only use the scavenger construct + animovore combo early on, or before a necrogeddon. as a general rule you don't want more than 2 units you're surrounding stuff around at a time, having scavenger constructs, witch doctors and rot eaters at the same time will crowd things, so when playing, pick 2 of them, not all 3. Soul steal, Nuru's needle, Languid and Brain lice are there to control the board, and blightseed is there for ramp. Use Ilmire tribesman as a meat-shield and nothing more, and darklings to finish off idols when you're locked out of a game. Infectious Blights, more harvesters, and maybe a watcher or two are good things to spend money on to improve this deck further, as well as most the other stuff you find on Mono Human Decay lists, as that is what this deck is trying to be.