Complex sentence: As he grew older, he eventually became part of the criminal underworld when he was trained by Shredder as his bounty hunter and a master of all weapons, collecting them from most warriors he defeats.
Split into simpler sentences: As he grew older, he eventually became part of the criminal underworld when he was trained by Shredder as his bounty hunter. He is a master of all weapons and collects them from most warriors he defeats.