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By the way there are exactly 666 bredable pokemon. Of those you get 664 eggs because you can't breed the ghost bug type that has one health. That is a double Pokemon at level 20 for nincada. Can't get it through evolution normally. As well as Manaphy only breeds Phione, and Phione with ditto only breeds Phione as well. Hence 664 eggs.
By the way there are exactly 666 bredable pokemon. Of those you get 664 eggs because you can't breed the ghost bug type that has one health. That is a double Pokemon at level 20 for nincada. Can't get it through evolution normally. As well as Manaphy only breeds Phione, and Phione with ditto only breeds Phione as well. Hence 664 eggs.