There are a lot, I'll put a bit of my experience of use.
- Goat zinka: my first mpunt in game, I used it on lvl 3 to be faster on cc, while doing 113 quest. Speed is important at that lvl if you want to complete the agudar feat.
- Crion zorb: my second mount, on lvl 4. I used it for mercenary quest, village patrol... to hunt naked some dogs lvl 3 at vurdaliya (yes, I wanted to hunt naked already in lvl 4
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)
- Poisonous crion zorb: to do arena, and arena's feat... I did fast purple badge of uk, just doing arena with my poisonous. Really good and fast way to earn reputation and complete arena agudar's feat.
- Battle zorb: I used to hunt with it on lvl 6, it kills without you doing damage, and you earn drops/few money without experience.
- Endagar/Shankar/Anlagrisa/Zeradar/Scorpolion: lvl 10 mounts that can be transformed into lvl 13 or 16. Are the mounts you will use the most during the game play. For everything, from instances to battlefields or quest. Several uses, and each one has it's favourite one. Zeradar or scorpolion cost less to invoice, and are strong powerful ones so everybody wants them. Anlagrisa is just for girls, and endagar or shankar can be achieved by reputation. In my case: I prefer endagar to fight a lot of mobs because with it cast does much more damage than any other mount in same situation, anlagrisa just to walk around to be cute xD and shankar... just because I love cats
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As I said, this are the "popular" mounts so everybody has their own way to use them
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- Jackaral: can be also lvl 10 or 13, bloody or purple. Purple jackaral does a cast that put poison on the enemy, so is useful on low lvl's to do palace for example and be able to kill magish. Or to fight long live mobs, because you can jsut stall until poison kills it. Not so useful against humans because poisons don't do too much damage, better for quest/mobs. And then we have bloody, that does a cast that makes your opponent hit just by 1. More than that, every 3 low cast, it quits 500 hp, that is a lot. So for me is my favourite one to use on battlefields, really strong mobs, or complicated quest. Is just not useful when your oponent has antichaos scrolls, in that case better use one of the other mounts.
- Ellan/Tuver: I use them just to be cute while walking xd
- Polar bear: can be lvl 8, 10 or 13... I used it to hunt naked until lvl 9, the bad part is that use snowballs as food, and you don't want always to go there to pick. Good point is that food is free.
- Vargash/Corvus: same as polar bear, but this ones eat normal food for mounts. They were really useful to fight when I didn't have a lvl 10 mount. And they are useful for cerberus event, because you can't use any mount bigger than lvl 8.
- Lagmur: The only mount that can help underwater.
Sure I forgot a couple, but based on my experience this are the mounts and how I use them.
Cheers.