From Battle of the Immortals Wiki
Getting Your First Mount
Shortly after arriving in Atlantis, your character can visit Knight Elder Mistra and accept the Manipulator quest to kill Hannibal in the Knight's Jail. You can be as low as level 20 to complete the quest, but you will not be able to use your mount until reaching level 25. The quest will reward you with a Common Mount Token. Right-click on the Common Mount Token in your inventory to receive your class mount. Each class of character receives a mount suited to their particular style: the feral Berzerker gets a Dinosaur, the noble Champion receives a Charger, the vicious Slayer a Direwolf, the Magus a Darkcharger, and the outcast Heretic rides a swift Ostrich. Right-clicking the mount in your inventory will add it to your mount interface, which can be accessed by pressing "z" or from the Pet window. This is just one of the many mounts available in-game. You can also purchase different mounts via the ZEN Marketplace and obtain them from various sources (see list).
Click on the Mount button in the mount interface to summon your steed, and click Dismount to dismiss it. There is also an icon in the Special Skills window that you can drag to your action bar for rapid mounting and dismounting.
While mounted, your movement speed will be increased but you cannot participate in combat. Additionally, you will receive a class-specific buff while mounted that will persist for 30 minutes after dismounting. Make sure you mount up every so often to maintain this boost, which will give you an edge in combat.
Main article: Mount Upgrades
Upgrading mounts not only improves their stats, but also gives you a different mount graphic for each level of fortification. To fortify your beginning mount, you will need one or more Common Mount Gems. You can immediately get these from the Marketplace, but they are also given as quest rewards after you reach level 30.
The easiest way to get some Common Mount Gems is through the level 30 God's Guide quest series, which begins at Dhocky in Atlantis Square. After running around to a few NPCs, you will get three Common Mount Gems from Mount Trainer Maelor. You will also get another Mount Gem from Berminham for completing the level 31 quest "Search in Seas" as part of the main Scenario quest line. Agamemnon gives you this particular branch of the quest.
Now that you're armed with three or more Common Mount Gems, you can get down to fortifying your mount to improve its Grade. Open up the mount window and make sure you're dismounted. Then click the "Fortify" button below your mount's image.
Reaching the first fortify grade is not that challenging, you have an 80% chance of success. The chance to fortify your mount decreases as you reach higher grades of quality. Any failure will drop you down a grade, so don't get too greedy. Grade 2 is a good starting goal. After a success, you will see a star added next to your mount's Grade. You'll also see your mount's graphic change to a more advanced form.
Later on, when you've gotten many more Common Mount Gems, you'll be able to get your mount's grade up to the maximum of 4. Reaching this achievement gives you the additional benefit of mount-related skills. The icons for these skills will appear in your mount window and can be dragged to your action bar like any other skill.
As you progress in your adventures, you will be able to tame new categories of mounts. The next class of mounts are Elite Mounts, such as the Snowbear of the far north, which give you more skills. Eventually, you may also obtain a Multi-Player mount like the Behemoth Chariot, which allows you to transport your buddies along with you. These advanced types of mounts require special gems to upgrade, but the rewards are certainly worth it!