Hehe, well you'll definitely need a second Pokémon he's compatible with, which probably goes without saying. Oh, but what might not go without saying is that it doesn't have to be another Zigzagoon. In fact, in some ways it's almost better to breed cross species pairs. You won't wind up with a new species or anything, but sometimes the dad will pass down moves to the babies that they can't learn any other way!

Every Pokémon belongs to either one or two egg groups and its those groups that determine what other species they can breed with. It should all be in your manual, if you haven't gone through that already.