Nightmare is actually a pretty good attack. Fully maxed, it does 520% intellect! That's the most straight damage a Psycho can do with one attack. Now what I suggest you do with this is to chain it with Wraith Form, then use Nightmare, and then let loose with Corruption. Corruption works with any shadow buff or debuff with no cooldown, so the damage you do with corruption overrides any damage they recover at all. Nightmare's health recovery is actually not very great.
Psychos are very hard in the starting game, but once you get their abilities down, they are extremely powerful. I agree with your guidelines, but I have a little different view on Retrograde. Normally, it's trash. Use the slot for something else. However, during the Baron fight, it will save your ***. Before the Baron fight, re-spec and get Traumatize and Retrograde specifically, I beg all psychos.
