I saw all those people saying Nightmare is crap, but it actually isnt (fully evolved). I mean, 520% of you instinct is very much, and if the enemy is not dead just use shock therapy to negate the healing effect of Nightmare. not to mention it is good for finishing strike.
yeah, if you have higher speed than them you can use subversion one turn, then use nightmare on them for the secodn turn to do the main healing. the status effect will still heal.
I have found that the Nightmare aftermath is not dispelled by Corruption, so it allows attacking the nightmared creature over and over. So if you don't want Overdrive, you might use Nightmare as a substitute to Epiphany in terms of delivering Corruption.