To tame a pegomastax:

Have any type of berries and put them in your last slot, after, have nothing on your shoulder and walk to it slowly and let it run at you and steal the berries, then, put more berries in that slot and walk to it slowly and feed it and keep repeating the same thing until he’s tamed. If your far from your base have some cryopods and put him in it. It’ll be gone because it jumps in your face but is on your shoulder the whole time!