Every team needs its muscle, and for the HIVE, that's Mammoth. You could argue that of all the villains in the main HIVE group (or at least the original 3), Mammoth got the least spotlight.
I grant you, he's not the most compelling character, at least not in the show. He's shown to be the muscle and nothing else, but trust me, that muscle is plenty. He's gone toe-to-toe with Cyborg and others and has had muscle to spare.
So trust me, this is one guy you don't want to make mad.