Hi guys, this is my first time posting on this board and I'd just like to ask a quick question.

So I recently started playing Pokemon Crystal, and I caught a Gastly early on. Its moveset is as follows:

Hypnosis
Lick
Leer
Mean Look

It's trying to learn Night Shade as I type this. Which move should I ditch in favor for it?

Also, I have the Nightmare skill in my pack, is that any good? If so, which move should I ditch for that?