Werewolf hybrid
Though not in the twilight seires and very rare the werewolf and vampire hybrid is one of the most powerful creatures on the planet.
These rare hybrids are even more rare than their human/vampire hybrid cousins. And they can not be made by a vampire and werewolf biting a human at the same time (that human will become a werewolf because their venom is stronger than a vampires and will kill the vampire venom), nor by a male vampire and female werewolf mating. The only way to make this type of hybrid starts out the same way as a human/ vampire hybrid is made.
A male vampire must impregnate a human female. And she must be unprotected during the full moon, and she must be bitten by a Child of the Moon and survive. She would then become a werewolf…