Hi there ! This is my first time posting something, and I would barely call it an exploit (more of a bug), but it works, even if I don't have a screenshot to prove it you can certainly test it yourself.
When I was in the cave right before defeating Tortos, I fell down in the water and noticed I was able to use either my Life-binder's Handmaiden or my Standstone Drake in the water. I could ''swim'' with it, but once I was getting out of the water it would dismount me.
I don't know if this works too in the water right before Megaera, free to you to try it out !
This reminds me of the bug that allowed me to fly in Throne of the Four Winds with any of my flying cloud serpent (wich is now fixed) :
Attachment 14765
Hope you enjoyed even if it's kind of useless^^
- Kalt