Play through the original Red Version story with a twist--you can steal trainers' Pokémon.
Rules:
1. Poke Balls, Great Balls, and Ultra Balls are now named Thief Balls, Robber Balls, and Burglar Balls.
2. You can capture trainers' Pokémon using those balls.
3. You cannot capture wild Pokémon.
4. Your Pokémon do not gain experience.
Yeah, the idea of stealing pokemon isn't new. But I think the idea of forcing you to use only stolen pokemon that don't grow stronger is new. If you play it, let me know if it's actually fun. I can imagine it being pretty difficult later on, but who knows. Maybe I'l even play it. *gasp*