Ok, for those of us people who cant seem to get any pearls for a tuso to simply grab on a mosa and wait it out then i have a solution. Down in the depths there is a cave on the ragnorok map. Some call it pearl cave or mushroom cave. Either name works. What i did was i mad a crap load of tranq arrows, took a journeyman crossbow and a 227 meg (not neccessary. You can have any level an icthy works too) and lured a mosa into this cave. When you enter there is a fork in the path. Take a right and you will notice that the land comes up where your meg can get through but the mosa can't. Camp there with your crossboe and tranq it. Stand on land so you dont waste the scuba tank. Once it runs it should run into the wall that is opposite from the middle island. After its out grabs some narcotic and meat. I reccommend setting up a little FOB or mini base at the cave beforehand so you are prepared. Wait it out and enjoy your new underwater giga!
Besides the giga this is the hardest dinosaur to tame, note you will need a lot of narcotics and food. Before you begin the tame I recommend at least 2 to 3 full scuba suits for obvious reasons. You need to have at least a Ichthyosaurs or Megalodon, so you can actually move around and find a decent one. Once you find one you want to tame simply start shooting at it with the crossbow. Now right when you get his attention swim up, you should notice the Mosasaurs stops following you after a certain height. The Mosasurs cannot go higher than wherever it stopped. So simply park your water Dino above it and keep shooting it. If it runs off keep doing the same thing over and over again. Sooner or later you will take him down. Good job! Then simply use this app to figure out how many narcotics/food you will need to tame it. Once it is done enjoy your king of the water.
Go Deep In A sea And Find Mosa.Then Prepare Your Ascendant Bow And Shoot The Mosa.Then Ride On Megalodon And Go Far From mosa Then Once Fire on mosa Do this 10 times you will able To Knocked out 320 lvl Mosa Then Tame it.
Heres how me and a friend of mine tamed it (you can also do this by yourself). Make a bird cage trap made out of stone as they dont damage stone structures. When its trapped, just tranq it with the weapon of your choice.
To make a bird cage trap, youll be needing 4-5 Behemoth Stone Dinasaur Gateway, 1 Reinforced Behemoth Gate, and a couple of stone pillars.
1st, decide on where you want to place the trap, I recommend to place it at the bottom of the ocean.
2nd, place the 1st gateway and put the 2nd in front of it, and so on. Make sure to make a little gap in each of them.
3rd, place your gate at the one end of the trap and the pillars on the other end. Make the gap of the pillars wide enough that an Itchy can slip through.
4th, luring the Mosa to your trap, I suggest to use an Itchy. Grab its attention and lure it to the trap, before you do this make sure the gate is open, just go right inside the trap while its chasing you, exit through the back end of the trap. Trap it, Tranq!
More over on the dlc you would have pocket of space where you could create tools and have a breath of air there would be creatures that could give you water similar to oil bugs. With vents that would go and shove you upwards. The new creature would be a thing that would set up deep sea areas and required food to be dragged towards it similar to otters they would speed as super sonic speed and inflict a deprevention debuff that starves you of oxygen. It would be able to morph into the ocean floor or the top to hide itself
best way to tame this thing get a low lvl squid with points on health hold the mosa with squid and go up and wait 15 the mosa ko by the way if you get the mosa up the mosa will leave you and not attack you just wait the mosa ko if you find this help rise it
There is only one way to tame it in PC version but Mobile version have two ways. First way, Go with Basilo or Itchy and tranq it in the ocean. I suggest Basilo because Electrophorus can stun you and ruin your adventure. Must take Scuba with you.
Second way, This is only for mobile players.You must have a Revival platform. First kill the mosasaur by your strongest water Mount. Don't harvest the body and take the Implant from it. Then place the Revival platform in water which must be deep enough otherwise your mosa will resurrect in Air and get killed instantly.