>>51301893>>51302468ghost and dark are both separate types for exactly the same reason why anyone is an idiot for merging rock and ground together: ghost and rock both imply specific physical properties of a monster who possesses them. a ghost type needs to be immune to non-elemental attacks but a dark type does not, the same way a rock type needs to be resistant to them but ground types do not.
if you made houndoom into a ghost type, you are an idiot. if you made houndoom into a normal type, you are also an idiot. it's that simple.