Jellyfish mounts

Jellyfish mounts were first added to World of Warcraft with Legion.

Drop

 * Surf Jelly is a potential drop from Island Expeditions.
 * Ny'alotha Allseer drops from N'Zoth the Corruptor in Ny'alotha, the Waking City on mythic difficulty.

Quest

 * Fathom Dweller is a potential reward from DANGER: Kosumoth the Hungering.

Professions

 * Pond Nettle is fished from the waters of Argus.