It depends on what pokemon you're breeding with. If the daycare man says something like "the prefer to play with other pokemon" then the pokemon you're breeding with isn't compatible with Pupitar. It has to be in the same egg group as him or you won't get an egg. If he man says anything else, then they will breed, but some eggs take longer than others. If you aren't sure how the egg group system works, try breeding him with a ditto, who can breed with any pokemon capable of making an egg. If you're trying to get a larviatar, also note that Pupitar has to be a female, unless you're breeding with ditto.
