Guys its easy to knock out Mosasaurus just use tranq harpoon arrow it gives so many torpor if u shot from the head anyways craft 3 behemoth gate and a 2 behemoth reinforced gate when you find a mosasaurus just stay back a little bit and build the trap get your small creature like itchy or if u have 300 health and using flak armor get him tot he trap and close the gate thats it you can finish him off easy