Catapult and boulders, make sure you're trap has doors on it so other players can't kill it while you're taming it, even on pve... 5 dino gates and 1 behemoth gate is perfect. No spaces in between the dino gates. Pillar 5 high for the catapult
Tranq Arrows/Darts DO NOT WORK!!! To knock this out you need to use a catapult and shoot in only on it's back. If you shoot it on it's legs it will kill it. UP-VOTE SO EVERYONE KNOWS & TO GET DODODEX TO ADD THIS!!!