Short Answer 
The Crimson Death Charger mount in World of Warcraft is exclusive to the Death Knight class, requiring players to fulfill specific achievements and milestones related to that class. Other classes, such as Priests, cannot obtain this mount and must play a Death Knight character to access it.
Step 1: Understand Mount Class Restrictions
In World of Warcraft, mounts are often categorized by class restrictions. The Crimson Death Charger, in particular, is exclusively linked to the Death Knight class. This means that only characters of this class can obtain and utilize this specific mount.
Step 2: Recognize Class-Specific Achievements
The Crimson Death Charger is awarded for completing unique milestones tied to the Death Knight class. These achievements may include reaching certain levels or completing specific quests related entirely to Death Knights. As such, players need to progress through the Death Knight’s dedicated achievements to earn the mount.
Step 3: Know Your Options with Other Classes
If you are playing as a Priest or any other class, you will not be able to obtain the Crimson Death Charger. Instead, each class has its own unique mounts. To ride the Crimson Death Charger, you would need to create or play a Death Knight character and fulfill the necessary criteria:
- Progress through Death Knight questlines
- Achieve class-specific milestones
- Reach appropriate character level