Not v hard to tame not even hard its mid hard only here is my setup to get a low level one easily ( 6000 hp rex 1 long neck rifle 1 bow or cross bow 30longneck bullets some arrows ) kill a male one with ur rex or ling neck lure another one to a safe place with an argy where ur rex is in let it hit ur rex set ur rex to passive and shot it with longneck and bow until it is at 10% hp ( u can do the math ur self ) then wait till ur rex is infected by the rhynio and it run away and full its craving till the timer ends it can ask v v ordinary and rare things also its ur. Choice to feed or not effecrs the level that will come out from baby one then just see ur rex die ( DONT HIT IT IT DOSDNT SPEED UP THE PROCESS) then here u got a rhynio baby take care of it and u got a monster who can carry half ur base in its inventory and carry good dinos and big ones also like diplodouces rexes spino ( no bronto no bigger than that )