Ditto-Breeding Ditto-Breeding
Ditto-Breeding. Ditto can actually be quite useful in battle too, seeing as it copies the opponent's stats (including stat changes) and moves. It can be surprising
Bugs-Begining(Gotsta start somewhere). Not all bugs are only good in the beggining, even Dustox can be useful later in the game (or in Netbattle), if used right. (it's a nice Toxishuffler ^________^)
Castform-Many stategy possibilities! I agree, and I partly agree with YoshiRiRu about it being strong enough to take advantage of them, but with the added effect of Rain Dance, Weatherball and Thunder can do some serious damage on a Castform (Weatherball alone is quite strong, now let's add in the STAB and Rain Dance bonus, and let's not forget about Thunder getting 100% accuracy from Rain Dance)
Rattatta etc-Start. I have to agree with YoshiRiRu, however, Raticate can do quite a lot of damage with a Choice Band
Plusle Minun-TEAMWORK COMBOS! They don't have enough physical defense, Snorlax (or any other Special sponge/wall that uses physical attacks) would screw them over easily
Porygon-Can Be Good Not only can, but it is good -_- Yoshiriru, I highly suggest you try finding out something about a Pokémon's stat line and movepool before you say it sucks
Spinda-THERE WILL BE ONE I believe I already said what I have to say about Spinda earlier
Corsola-LEARNS RECOVER SO CAN BE POWERFUL! It doesn't have enough defenses or HP to take full advantage of Recover, most Pokémon will OHko Corsola or put it in the red zone with one attack, so Recover is practicaly useless here