Ghost Dash chains off from Another Chance so, to my understanding, it'll only come into play when you hit 0 HP and Another Chance triggers. What, exactly, it does is an unknown to me though. Faster dashing while dead (or no MP cost)?
The only time I've died while having those two learned was when I was messing around with a Bone Shield (-30 HP) and had no opportunity to try it out. If you have no MP while dead, then it's probably what I guessed. Something to test out later on.