What do you mean? I can agree with Plusle and Minun, but Pichu? He was perfectly reasonable at the time. Gold and Silver had just come out, they needed a gen. 2 rep, and what would be better than the pre-evo of pokemon's mascot? Anyways, I thought Pichu was a much better idea than G&W, who's inclusion still puzzles me a little to this day. Of course now they need gen. 3 and 4 reps, and Pichu wasn't needed anymore.
BTW, I consider Pokemon Trainer as the gen 3. rep, for a couple of reasons:
His design is based on Firered/Leafgreen design, which was released in gen. 3
Bulbasaur, Charmander, and Squirtle are the starters of FR/LG
His green costume is colored like the Emerald version clothings of the R/S/E heros, which again came out in gen. 3
Yeah, I'm a poke-freak.