Have 2 b skulls and was curious so I tested it. This 100% works, under the card effect. You cannot summon from the extra deck, only the graveyard, so it ~technically~ works. If you have one b-skull in the graveyard, and summon a second one, you can use palabyrinth to revive the dead one, that's it. Anyone know of possible future cards that would allow you to discard from fusion deck?