I have a giga. His name is Anguish. Anguish loves to go out on "strolls", where he kills everything in sight, manmoths, rexes, rhinos, deer, wolves, and much more (I live in the north, right next to white pillar and right above a cave). We come across an alpha rex while on one of our strolls. Me and Anguish decided to kill the alpha rex (Anguish is lvl 435, because we have Ascendant Creatures.), and Anguish totally demolishes the alpha rex. I got a pretty cool trike bone helmet skin, and I applied it to my ascendant mining helmet (I wear full ascendant)

Tldr: Get a giga right now.