Mysterious Ticket

The Mysterious Ticket is a ticket that allows you to access Birth Island by talking to the Mysterious Captain at the Vermilion City Harbor. You have the chance to encounter all of the Legendary Counterparts that you were not able to capture previously. Keep in mind that you have to capture at least one of the following Legendaries in order to be able to catch its counterparts on Birth Island:

Azelf, Mesprit, Uxie | Entei, Raikou, Suicune | Latias, Latios | Regice, Regirock, Registeel

In order to balance out this awesome opportunity, you have about the same chance to encounter a Legendary as a Pseudo-Legendary, which will have its Hidden Ability. You can encounter one of the following Pseudo-Legendaries:

Dragonite, Garchomp, Goodra, Hydreigon, Lucario, Metagross, Rotom, Salamence, Tyranitar, Volcarona, Zoroark

These available Pokemon cannot be shiny on Birth Island!

Once you enter the Birth Island, your Mysterious Ticket will be removed from the inventory and one of the Pokemon above will spawn. Until you capture the Pokemon that was spawned, run away from it or faint against it will remain on the same spot. Therefore, you can leave the island in order to get Synchronize Pokemon from the Pokemon Center or to buy Master Balls.