How I did it high lvl plesiosaur and mosa have it Agro the plesiosaur and let it grab on then go into feed it put the plesiosaur on follow and bit the squid once or twice with the mosa should make it let go of the tame then just go up to the depth limit till it's time to feed again and just repeat till tamed (caution: this can be very glitchy)
Use a Mosa to tame this beast. Let the Mosa get grabbed wait a couple seconds get off feed it black pearls. Have your mosa on follow lowest, swim a bit away from the Tuso after feeding it, when the Tuso lets go the Mosa will swim to you. Repeat until Tuso it tamed. Super easy!
You need two people, one for feeding the black pearls and the other to feed the turtle that is in the grasp of the Tusoteuthis, with sweet vegetable cake for the health and to feed it stimulates berries as well
Don’t let it grab your tame when near the ocean floor. It’s mechanic while holding your tame makes it tilt in such a way that you are moved underground. Then the game rerenders you and your tame above the water. Lost a lvl 218 mosa instantly. Try and get the squid to go a little higher before trying to tame.