i've been breeding a male gastly with an impish nature with a ditto for 2 days and have hatched a ridiculous amount of gastly eggs and have gotten probably every nature except for timid... any reason why this is happening or am I just extremely unlucky?
It is possible to get a Timid Gengar. You are just extremely unlucky. Keep on going and you will get one eventually.
If the gastly has an everstone, it won't work. Otherwise, see if you have a Pokemon with Synchronize. Put it at the head of your party, and search for Gastly/Haunter/Gengar. If you don't have one, I'm sorry, but I don't know how else to help you.
Hope I helped!
Source: Vast Knowledge