Small/Big Gnar vs Mini/Mega Gnar
I feel the Mini/Mega words are too sophisticated for a prehistoric creature to use. For me they feel alien, they don't deliver the prehistoric theme nor the savage theme.
Small/Big are way better in this situation, since they are simpler words, not modern nor sophisticated, the "big" sounds savage too.
Go ahead, just shout it out loud:
"ME MEGA GNAR! GNAAAAAAARR!"
"ME BIG GNAR! GNAAAAAAARR!"