Booming Blastoise, in keeping with the anime theme, take a Butterfree named "BeFree". You can only teach it the following four moves, which will be its moveset for the entire time you have it*:
It must solo Misty's Starmie with as much of this moveset as it has at the time; any other moves cannot be used.
*I say "as long as you have it" because, yes, you will complete the similarity between the game and the anime by releasing BeFree just before Saffron Gym. In honor of BeFree, you'll keep the spot it used to occupy open, never replacing it on your team.
If you find you can't bear to send BeFree away, then you must immediately change its nickname to "Trapped" and you can no longer use the same move twice in a row. In addition, it must remain in your party at all times and cannot appear in battle until all of your other Pokemon have appeared at least once. At this point it may learn Psybeam, but can only use it once per battle (Psychic is banned at all points).
Good luck, and choose wisely.
14:15 Ragnarokalex i do believe its time to hit some children with sticks