Class Mount
Spiritual Guidance: Diving into The Sunken Vault for your Priest class mount
Everything these past 11 weeks has led to this.
Lightsworn: Stirring in the Shadows for the Paladin class mount
If you've been dutifully plugging away and finishing all the special Broken Shore weekly quests up until now, you should have earned Breaching the Tomb for completing the Legionfall campaign.
The Warrior’s Charge: The Trial of Rage scenario and your new class mount
The new class mounts tend to work in a certain way: You finish the long campaign to open the Tomb of Sargeras, you are challenged to complete some sort of event, and when you're done you attain a mount.