I was taming a mosa with my friend and 7 of these of the these underwater giraffe cat eels came at me like the Texas chainsaw massacre guy just as scary too. What I’m saying bring and army of megladons and mantas
After tamed, you can grapple onto them while a tribmate drives it and easily tame more large water mounts. If you are about to touch a structure or terrain, crouch to take off the hook or you will die instantly and your body will fly across the map
The trick to ko these guys is to wait for them to agro you, once they're close enough, swim up and backwards until you've reached their swim limit and shoot them as many times as possible. When they lose interest, just do the same trick and eventually you'll knock it out
If you are being chased by a plesiosaur,then swim up to the surface.like the mosasaur,the plesiosaur does not swim over a certain depth limit and is never seen at the surface(bit weird since they need to breathe,right?)
There is an invisible barrier at a certain depth that the plesis will not cross, you can drag them up to this and shoot them till they deagro, when they do reagro and repeat until their knocked out. Also, you can drag them to the entrance of an underwater cave, and shoot the plesi, as long as you dont venture too far into the cave, it will not deagro.
Beefy, powerful, fast, good lifter, supports platforms, can be tamed on foot with much less efort and risk than Mosas (still not easy). For sure this thing is the most versatile mount after Mosas, Quetzals, Wyverns and Mantis (oh boi, you NEED a Mantis).
For Ark Mobile: get urself a basilosaurus if u can't unlock the scuba set. Find it and then stay a little bit away from it and it can be done easily with tranquilo arrows and a crossbow. Get some Rex kibble or meat
Since a certain update, you can no longer get the plesiosaur to chase you up until it can't reach. When it can't chase you anymore, it will run away every time. Bring a dunk and let it munch on it against a wall. Especially on Ragnarok, the ocean is very open on there.