if you want to kill a titan, try to lure him into the sea and attack him with mosa (At least with 600% + damage). and when his life is below 50,000, he will run from you. then use the quetz (or Other flying Dino) and run in front of the titan and he will come back into the sea again, continue to attack him with mosa and repeat the steps above if he is out of the water. I usually use this technique when I want to level up and it works