I won't get into much detail about the story, I just need help with my team. The team is as follows;
Pikachu (He started the team and is therefore the leader, he's also pretty powerful as he's done a lot of training)
Scyther (He's a powerful fighter with his scythes, is really fast, and he'll be able to fly short distances)
Castform (She's the member I'm not too sure about having, but her ability to change the weather would be useful to the team)
Cubone (His bone will be brilliant weapon, as he can hit enemies from a long distance with his Bonemerang attack, or close-range with his Bone Club or Bone Rush)
Combusken (He's another powerful fighter with a combination of fire and fighting attacks, I also plan on making him knowledgeable about food, including berries and seeds)
Chikorita (With moves like Aromatherapy and Synthesis, she'll be a great medical help to the team)
Absol (The ability to predict disasters will make her an important asset to the team, and she'll also be a skilled fighter)
Metang (I plan making him a good weapons technician, being being able to make weapons and orbs for the team)
Haunter (His ability to walk through walls will useful, and he'll also be entertaining to the team)
I might add some more members later, but that's the team at the moment. Anyway, I'm happy with everyone except Castform. A running theme in the team is the potential to be strong, seeing as how all the team's evolutions are extremely powerful (minus Absol and Castform who can't evolve). Absol is powerful anyway, but Castform just isn't strong at all, and she'll stick out from the rest of the team. The only thing that still keeps her in is her weather abilities, which I think would be really useful to the team. So, should I keep Castform, or should I replace her with another Pokemon. Any Pokemon from any generation is fine, apart from Water-Types. I'll probably add a Water-Type to the team later.
You might be approaching this the wrong way, as in the end it's less what Pokemon appear in your fic (within reason of course e.g. a zangoose and seviper aren't likely going to be best buddies for instance), and how you use them and what they do themselves. Don't worry too much about stats Pokemon may have and consider how useful they will be. Castform I would be imagine would be very useful; manipulating weather sounds like it after all. What if the team's suddenly in a desert with a sandstorm? Problem solved by Castform, and everyone benefits.
And not all Pokemon need to contribute to battles by being physically strong to be useful, but I suppose if anything that's a neat thing you could actually explore in your fic. How does Castform feel in being the odd one out? What about the other Pokemon? I'd say that sideplot would be interesting to play around with and also to read about. There's always that side of the matter after all; the team doesn't have to work perfectly together, and if anything it would be more boring if it did.
Agreed, stats are pretty much a game thing, so they should be more reference (a magickarp tackle should never amount to a tackle from a swampert). Castform is pretty good as a pokemon because usefulness and strength are not the same.
Think of castform as some sort of white mage, without the healing.
Well, Bob makes a good point in that the side plot, if done right, could be quite interesting.
You could also make her a strategist, or tactician. No matter how strong the team is, if they just run ahead madly into the dungeons then it'd just be chaos.
Another part of it is that diversity of character is always a good thing.
As well as the fact that it wouldn't be much of a story if they never had any difficulties to overcome, and with multiple character types you have far more options for scenarios and how they overcome... or don't.