I suggest getting onto a cliff, spam tranq and start chasing it. I can easily do it on a lv 150 Spino at a river on mobile and remember to surround it with spike walls and camp your Spino, or just render it out while it was taming (just make sure it is guarenteed to be tamed afterwards, and feed it soothing balm on mobile if possible). After taming, you will feel unstoppable even against trex. Easiest endgame dino you can get.