I recommend stop listening to the passive tame bs and do the knockout method. All you need is to build three behemoth gateways with only two of them having gates. After words, lure the megachelon into the trap and place the final gateway down. Finally there is two options, you can either lure the megachelon onto land and trap it while using a longneck to its head, or get on its back where it can’t hit you and use electric prods bc they bypass all armor. DO NOT USE CROSSBOWS OR SPEAR GUNS, THE MEGACHELON WILL DIE.