WoW Achievements — Browse All Achievements
Track all 8,600+ World of Warcraft achievements. Browse by expansion or category — Dungeons & Raids, Quests, Exploration, PvP, Professions, Reputation, and more. Sync your character to see completion progress.
Browse achievements from all expansions including The War Within, Midnight, Dragonflight, Shadowlands, and Classic. Find guides for Glory of the Raider, meta-achievements, PvP achievements, exploration, and more. Track your achievement points and completion progress via Battle.net.
Lord of the Reins
Obtain 300 mounts (usable by a single character).
Lord of the Reins requires obtaining 300 mounts usable by a single character, rewarding the Heavenly Azure Cloud Serpent upon completion.
Identify Your Best Character
Do not rely on your Mount tab (Shift+P) to track progress — instead, check the WoW Armory to see the actual number of usable mounts for each of your characters, as the count differs per character based on faction, class, and profession.
Prioritize Your Paladin
Your Paladin is likely to have the highest usable mount count, as they have access to three class-specific mounts: the level 20 warhorse, the level 40 charger, and the 
Argent Charger from the Argent Tournament for 150 seals.
Leverage Profession Mounts Account-Wide
Profession mounts such as Leatherworking wolves, Tailoring 
Flying Carpets, and Engineering flying machines learned on any alt will increase your Paladin's individual usable mount counter when you log into that character, even without having the required profession yourself.
Log Every Character to Check Count
Log into each of your characters one by one to let the game calculate each character's individual usable mount total, then determine which single character is closest to the 300-mount threshold needed to complete the achievement.
Tips
The achievement counter reflects mounts usable by one specific character, not your total account-wide collection, so the character with the most class and profession advantages will show the highest count.