The Mount and Pet available with the purchase of one of the collector editions of World of Warcraft: Shadowlands are now known: they are respectively the Ensorcelled Everwyrm and the Anima Wyrmling.
The Ensorcelled Everwyrm
The Ensorcelled Everwyrm is included in the Heroic Edition ($54.99) and the Epic Edition ($74.99). It's a flying mount available for both Alliance and Horde players.
The Anima Wyrmling
The Anima Wyrmling is offered as a reward for the purchase of the Epic Edition ($74.99). This is a pet available for both Alliance AND Horde players.
