Several things to take into consideration here:
1. You'll need to have a way to adjust your team level to a standard (usually lv.50)
2. You'll need to disable exp/money gain
3. You'll need to allow the player to lose battles
4. You'll need the Trainers to have at least two things to say after battle (message when you win/lose)
5. You'll need to have some sort of system, which creates random matches and rounds depending on what tournament you're in
6. You'll need to have an AI, which would decide which opponents go to the next round (you could do this by the type of Pokemon they use)
Don't know if simple events will do, for things like 1,2,4 you'd need to do additional coding.