Well, first off, I got a level one Spiritomb off the GTS a while back. I later learned that all of it's moves it didn't learn naturally. So I bred ALOT of them and trade them now and then (I have like 8 right now).
So here's it's moveset
Imprison (egg move from Ralts line) Pain Split (egg move from Misdrevius line) Destiny Bond (egg move from Ghastly line/ Wobbufet) Dark Pulse (TM move)
How was someone able to get all these egg moves on it? so how, and why, would someone breed this?
Male Gastly line / Koffing line / Wobbuffet learn Destiny Bond by level up.
Breed with female Ralts until you get a male Ralts, which has Destiny Bond as an egg move.
Level up the Ralts to learn Imprison.
Breed male Ralts with Destiny Bond and Imprison with a female Misdreavus until you get a male Misdreavus. Should have both Destiny Bond and Imprison.
Level up to learn Pain Split.
The male Misdreavus now has the 3 egg moves, breed with a female Spiritomb to pass all 3 moves.
Use a Dark Pulse TM on the resulting Spiritomb. Can also teach the male Misdreavus a Dark Pulse TM and have it pass all 4 moves. If Ralts learned Dark Pulse, it could be passed starting from the Gastly line, which learn it by level up.