I would do like this:
[Normal Mounts]: Simple mounts with low speed obtained through the lore of the game, quests until the end game.
[Rare Mounts]: Mounts with medium speed obtained by exchanging points or collected items obtained in automatic events or even by crafting rare items obtained in the game's dungeons.
[Unique Mounts]: Rare speed mounts obtained through unique events held on commemorative dates.
They could also be divided into Normal and Battle Mounts, the Battle ones allowed you to attack on top of them, the normal ones did not.
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At the game's Cash store, I would put cosmetics for these mounts, change of appearance, etc.