Why are Darkrai and Yveltal Dark type? Dark type are about fighting dirty. Darkrai's nightmare inducing powers and Yveltal's death (or destructive outside of japan) powers has nothing to do with fighting dirty. If anything, they should be ghost type. Ghost type fits the nightmare and death themes way better than the dirty fighter pokemon type.

In short, It makes no sense at all that they're Dark type, because Dark isn't literal darkness.