(Note: If you're not into reading, scroll to bottom of post for brief summary.)
I'm not talking about mounts that also work on water (like the broom or the cloud mounts), but rather a water-only mount. Here's what I'm thinking:
A mount that you can only ride in water (shallow as well as deep). I'm thinking its speed would be that of a regular mount at 3 bushes (give or take). Or its speed mechanics could work similarly to regular mounts, in that it starts at 0 and needs to intake something to get up to 5. Perhaps its speed meter automatically increases to 5 while over shallow water, and taking any damage would decrease 1 point of speed (like the current mount system). I'm also thinking it could only be boarded (and de-boarded) in shallow water. More patches of shallow water would probably need to be added.
Now, to explain what makes it advantageous to current mounts that fly over water. Firstly, you'd be able to swing your sword whilst on the water mount, attacking other players also on water mounts (but not players who are in the water with no mount), and maybe even.. water enemies? Second, you'd be able to use your net while on your water mount (I read another thread suggesting being able to use nets on mounts for this purpose, and liked the concept). This would of course make it possible to once and for all catch all those bugs that end up over water (especially in Oasis). Additionally, you'd be able to dive for loot while on your water mount.
As far as what these mounts would look like, I'm thinking the default models would be small 1-person boats. But, like with regular mounts, there could be a number of alternate types sold throughout time. Just think of any aquatic creature, really.
One other thing I thought of is perhaps a specific type of water (like maybe water with a strong current) that only water mounts can ride through. Maybe at some point when you guys are ready to release a new area, you can have it blocked by this strong-current water. And perhaps you would have to complete a quest to obtain your first water mount. You could tie it in with the zorbis, as it is water-related. Maybe it could be the continuation of the scarf quest, who knows.
I honestly think there's a lot of validity to this. I think it fills a need and could potentially add a lot to the game. Thoughts?
Edit - I know it's kind of long, but it's worth reading
Edit #2 - I understand that people generally aren't crazy about reading long posts. So I'll throw together a quick summary:
Brief Summary
Water mounts. Only usable over water, can only be boarded and de-boarded over shallow water. Has same speed mechanics as regular mounts. Speed goes up to 5 while over shallow water; is reduced by one when damage is taken. While riding water mounts you can:
-swing your sword (to damage other people on water mounts or water-specific enemies that could be added at some point)
-use your net (to catch bugs that are stuck flying over water)
-dive for loot
-ride over strong-current waters (which would be added in spots that are only meant to be accessible via water mount, like a new town, or even just a small hub)
Could be obtained via quest (scarf quest and/or tie in with zorbis). Original mount would likely be small boat. Different looks would be sold (or otherwise obtained) down the line; think aquatic creatures.