My intro:
I'm the last and strongest gym leader because I trained hard to get where I am in this world of Pokemon. I was once a trainer, but now I'm a gym leader trained by the old fart of the Elite Four that was once the Pokemon League Champion. I am Suijin Kyouryoku, apprentice of Akki Yokoshima, successor of Hatsu Tsurugi. My Pokemon are my friends, our bonds are just as strong as anyone who loves their pokemon, maybe even stronger. Do you have what it takes to defeat me? Do you have what it takes to defeat the Elite Four and become the Pokemon League Champion? We shall find out here today, but once you enter this battle you won't win.
My closing:
Congratulations on beating me. I was the last bump in your road to the Pokemon League. However, once you reach the Pokemon League, there won't be bumps there, but rather walls. You must find a way to go around them and face the Elite Four. If you win, you will be the Pokemon League Champion. Be warned though that the old fart still has more game than the new lot that are now the Elite Four. However, since you beat me, these walls are nothing, but mere small bumps, anyways, let me present you with the Universal Badge as a sign of your triumph over me. Also, let me give you my personal TM. This one has no number, the attack is called Shadow Inferno. Use it wisely, it's compatible with dark/ghost pokemon.
(The Old Fart of course is the secret boss, you know how in every game there is one? The old fart is the strongest boss you'll have to take on...how do you guys like the idea?)