In Genesis part 1 You can get him to swim into a bubble and it will be unable to move if the bubble gets caught on something (The Bubble eventually pops but it’s still worth a try, because the bubble still lasts a while)
All mosasaurs have a certain depth limit. If you find a mosasaur, lure it to a cliff side and let it get close, once it’s near you but not in bite range etc, start going up the cliff side until it loses agro. Once you find the sweet spot and the mosasaur loses agro, go down a bit to get in the depth limit range to re agro the mosasaur. It can’t attack you if you are just out of the depth limit range etc then start shooting it to knock it out. Just beware of other nasties 👌
Center tip: as they have added the mosa to the center I've found the easiest way to knock one out is find one close to the bubbles get its Agro and swim in the bubble the mosa will get stuck and it can't hit you. Also this gives you unlimited oxygen and sanctuary from being attacked by anything else. ðŸ¤˜ðŸ¼
In Genesis, there is a section underneath the Ocean E spawn where there is a glitch pass the big tek door that allows u to swim inside. I baited a mosa inside there and placed one behemoth stone gate down on him and tranqed from the top of where my base is on land shooting down on him. Yhere is currently another one there as we soeak but it's 4am and I make 9 lol
if you are trying to knock out an X-Mosasaur bring at least 3x the tranqs listed, X-Dinos take 3x less damage from you and your tames so as a result they require 3x as many tranqs. I went through 550 tranq arrows and 5.5 crossbows to knockout a 135 and it took 30 mins of non-stop firing so you might want to build a trap. Btw X-dinos also deal 3x as much damage as a non X-dino of the same species I believe so beware!