Well, I'm back. I've been in Washington DC for most of last week, so I had to make some quick fixes for this week. Let's take a look at your deck: 北北北北北北北北北北北北北北北
Pokemon(20)
4x Ditto
3x Blastoise
4x Squirtle
3x Lapras
3x Articuno
2x Khangaskhan
3x Seel
2x Dewgong

Energy(24)
21x Water energy
3x Double Colorless

Trainers
3x Computer search
4x Bill
4x Professor Oak
3x Gust of Wind
3x Pokemon breeder
The strategy to this deck is simple: Rain Dance energies to ditto. The reason Ditto can copy any pokemon. But in case Ditto, or Blastoise don't come out quick enough or there's a Muk on your opponent's bench you can use Khangaskhan to faint em' via a gust of wind. You need water energies to use, and the 3 double colorless are for retreating. As I remember from an issue of Pojo with a fossilized rain dance Lapras, and Articuno make good rain dance choices. I also remember Pokemon Breeder, Bill, and Professor Oak work perfectly in Rain Dance decks. Gust of wind, and computer search are also perfect.
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Overview

I see one problem with your strategy- under most circumstances, you cannot Raindance Ditto. The text on the card states that you can only Raindance Water Pok閙on. Unless your opponent's active is water, you can't do it. Ditto can still be used, though once Blastoise is out you'll probably have better options. You also have 65 cards, which I believe is illegal...

Pok閙on

You'll have to cut some here to get down to 60 and make room for other changes. I think the easiest way to do this is cut down on the Basic Pok閙on, they can be messed with without disturbing families and you have a lot of them. Drop one Ditto, one Lapras, one Articuno, and both Kangaskhan, which take a lot to attack, they can't be raindanced, and they've got a high retreat. Now you're back to 60 cards, let's move on to Trainers.

Trainers

You have extremely heavy card drawing, which is good but can take you very close to decking. Let's drop one Professor Oak, one Gust of Wind, one Computer Search, and add two Pkmn Trader and one Breeder. That should finish up your Trainers, let's go to Energy.

Energy

Since Ditto is really the only one that needs Double Colorless, and you're kind of short on Water, let's take out those DCE and add three Water.
Pokemon
3 Ditto
3 Blastoise
4 Squirtle
2 Lapras
2 Articuno
3 Seel
2 Dewgong

Trainers
2 Computer search
4 Bill
3 Professor Oak
2 Gust of Wind
4 Pokemon breeder

Energy
24 Water energy
I'm not the authority on Raindance, since I don't use it much, but I think it looks better. Hope it works for you, and good luck!

~ Souper ~