build a trap with 4 small metal archways and a behemoth archway, then kill 1 of your babyrexes, and drag him to him.. if he doesn't eat open the door and get him back in the trap. when riding only kill animals that don't do too much damage to you. approx. 5 times 20% taming step at x1. it is wise to put it back in the trap shortly before it expires. much luck