This deck is pretty dependent on it's general (mine usually are). The idea is to combine undying with effects which will make you able to sac creatures over and over and have them still come back, such as being able to remove +1/+1 counters from themselves, or coming into play with -1/-1 counters, which will cancel out the +1/+1 counter from undying.

Some win-con combos are Mikaeus + Triskelion for infinite damage, Mikaeus + Work Horse for infinite mana into Profane Command, or Mikaeus + any sac outlet + a creature with the above ability to come back again and again + either Falkenrath Noble, Blood Artist, or Blasting Station.