Ability: Voice Tuning (all attack moves known by Loudred and Exploud used by her get +2 damage)
Item: Microphone (cancels out all other abilities)
1. Hyper Voice
3. Sleep Talk
My own extra bit:
Where to find Avril Lavigne to capture. (a little humourous cheat)
Go to the top of Mt. Silver after you have first beaten Red. You will find Avril Lavigne fighting directly against Red. You get to watch the battle or skip. After the battle, talk to Avril and she will join you. Then talk to Red and battle. His Pokemon will all be at Lv 50. Avril will have an Exploud. Once it has fainted, Avril will fight by herself. You can do this over... and over...