Chifray doesn't use techniques in battle. He has a birth defect within him that causes techniques to "malfunction", resulting in tremendously overwhelming explosions. He was forbidden to use them by his father for his opponents' sake, not his. Disappointed, he came to accept it and learned to battle without. Just himself, his feet, his fists, his head, his tail, and his sharp brain.

Training extensively with such a limitation saw him learn a whole new style of battling. Becoming so able to read his opponents he not only recognized techniques and abilities as they came out, but he could also figure out where to strike for the most damage. This allowed him to take on monsterous rock and steel types, as well as Legendaries like Lord Dialga here.

It's simple. If he can't be hit, he can't be beat, and larger opponents are considerably slower.

He has beaten many a legendary in the past, and now they train under him because, as Legendaries, they have nobody really to teach them how to improve themselves.