Once you start walking through the grassy areas after the Victory Road door exit, you'll start to encounter some very high level Pokemon.

A couple new ones I encountered were Sneasel at night and Rapidash.

There's a Pokemon Center out here in the middle of nowhere, but luckily for you it will allow you to fly there later when you leave.

To the right of the Pokecenter on Route 28 there are two cut-able bushes. After them is a house. Talk to the lady inside and she'll give you TM 47, Steel Wing, for talking to her.

Blastoise can be taken out with a good Electric attack like Thunder or Thunder Punch.

Charizard can be taken out with a couple Hydro Pumps.

Try taking out Venusaur with a good Fire move or Psychic attack.

Espeon can be very dangerous to you, his Psychic attacks murdalized all my Pokemon the first time I tried to take on Ash. Try using Sneasel or Tyranitar since Dark Pokemon are resistant to Psychic.

Snorlax is Ash's most difficult Pokemon. However, if you have Haunter he would be really useful right about now, being totally resistant to Normal moves and all. Also, Haunter can take advantage of Snorlax always Resting by using Dream Eater. Ha! Take that Snorlax!

Ash will usually send out Pikachu first. Even though he's level 81, Pikachu can be taken out easily with a couple strong attacks. Dugtrio or Sandslash could be quite useful here.

After that you win. Ash leaves, credits role, and you'll get the Game Over screen again. After this you can still play on and on and on. Red will return eventually, so you can fight him again. There's plenty of Pokemon to find still, like the ones on the next page.