Yellow Pikachu can't evolve, meaning it's stuck with poor offensive and defensive stats for the majority of the game. Also, while it does naturally learn Thunderbolt, keep in mind that Pikachu's Thunderbolt is about as powerful as Dewgong's Aurora Beam or Magneton's Thundershock.
My Challenge Compendium
Current Challenge: Colosseum Scramble
Status: Prologue is up!
Warning: When things heat up in a thread, I usually chicken out. I also have the tendency to overlook minor details at times.