Ubers (dragapult, méga lucario etc...)

I always play in national dex classic so im not an expert. I saw that (for exemple) dragapult and méga lucario are uber and i was wondering how do you play them exactly? How can you make those "normal" pokemons viable in a categorie where every OP ahh legendary is allowed? I wanted to make an uber team and by curiosity i wanted to know how i could play those two, since it seems its the only category theyre not illegal (as far as i know) and as i think i understood, dragapult is pretty popular even if idk why.