If you use the bear trap strategy which is if you lead it into a Dino gateway that is shaped in a triangle and with a bear trap in the middle (Large Beartrap) and when it is stuck you must put a dinogate behind it to trap it and then knock out. (hope this helped and "If" I win could it be an Xbox voucher, thanks.)
When breeding two max level rexes to have a super baby, DON'T EAT THE EGG!!!! I've done this twice on accident(meaning to drop it) and each time it takes me a couple seconds to register wtf I just did and then I have to wait to mate again. Sad day. Weekend ruined. Great way to start off the new year! Lol
Create a 3x3 mobile taming pen 3 walls high on a raft with a Dino gateway on one side and ramps on the other. Use a flyer to lead it up the ramp into the pen then move it to a safe area to tame. I got 2 150s without a single issue.
You can use the normal darts or arrows. But the fastest way to tame a Rex .
Get under its belly as fast as you can and rub its belly, instant tame :) all you new player try it out and you'll be riding like a king like us vets !!
Since rexs are the second best land carnivore (behind giga) I would recommend just leveling it for PvP. Like on all my 150 kibble tame rexs I go for 10k health then 500 melee damage and then put the rest of my levels back and forth between health and damage.
PS: A good 2nd-5th gen Rex can and will kill tamed gigas