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This is my very best and favorite deck I call it the GHOST STALKER this is the name because there are Gastlys,Haunters, and Gengars in it and those are the main pokemon in the deck. The point of the deck is to get the Gengars out to use Curse and to use the Haunters pokemon power to stall, most of the pokemon in this deck have low retreat cost except the Promo Mewtwo's. It also has a Cyboard to beat Haymaker decks or Energy Removal decks, I will give you the Cyboard after I tell you the deck. Heres how it usually goes I use the Scythers and Mr. Mimes to stall the opponent while I build the Promo Mewtwo's and Ditto's up to full power then when the opponent is getting weak on the bench then I evolve to Gengar using the Curse to kill the benched pokemon and winning the game the potions and super potions are to keep the pokemon alive and plus powers to do the extra damage you need to win. So here it is my Pride and Joy deck!!!
GHOST STALKER

Pokemon

3x Gengar 
3x Haunter
3x Gastly(fossil alot better)
3x Mr.Mime 
3x Scyther 
3x Promo Mewtwo
3x Ditto

Trainers

2x Bill
2x Gust of Wind
3x Potion
2x Professor Oak
3x Super Potion
4x Plus Power
1x Here Comes Team Rocket
2x Computer Search

Energy

3x Leaf
4x Double Colorless
16x Psychic
Well thats that deck, and the Cyboard goes like this, this is to beat Haymakers or Energy Removal Decks ONLY
Take out  These Cards

3x Potion
3x Super Potion
3x Leaf Energy

Add in to deck

1x No Removal Gym or NRG
2x Recycle (since I only have one NRG if it goes away these are to get
them back)
3x Idem Finder
4x Goop Gas Attack (because most decks have Aerodactyls in it that
affects this deck alot so that stops that pokemon power)
So thats my favorite and probably my best deck try to get it revised soon please thank you very much.

Signed: Richie Marin of Worcester Mass.

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Overview

This fix is crossed with Ness, check it out at Ness's Nest =).

As for the deck... I think you mean "sideboard", but other than that it looks okay ;). Your deck looks pretty good, although there's always a bit of tweaking that can be done. The ghost line is nice, and you've chosen strong Pokemon to back them up.

Pok閙on

All you could really do here is play around with the numbers a bit, as they're all good choices. All I'd suggest is to take out a Mr. Mime for a fourth Gastly and drop one Scyther. Looks great!

Trainers

You could use a bit more tweaking here. First of all, I'd take out the Potions and Super Potions. Your Pokemon are strong, fast, and versatile, so you shouldn't need to worry too much about recovery. Would you rather remove two damage counters, or set your opponent back a turn, draw a new hand, search for a card in your deck, remove a damaged Pok閙on from play, etc? Potions just aren't the best options with so many good Trainers.

Here Comes Team Rocket can probably be dropped too. If you use a lot you'll be wasting all but one, since it's effect lasts the entire game. But if you only use one there's a chance you won't find it until you're almost through your prizes, or maybe you won't find it at all. Either way, the effect isn't really crucial and isn't enough to worry about.

With those taken out, we have considerable room. I'd raise the number of Bills, Oaks, and Com. Searches. Speed is good in any situation, not just Haymaker. You probably won't need a sideboard really, those are usually used in cases such as a mono Fire versus a Raindance- the sideboard would include some lightning or colorless cards to counter the weakness. You'll also want some Gym in there, and No Removal Gym should work. A couple of Scoop Ups for getting out of tight spots and a couple Item Finder should finish the Trainers. Should look about like this:

4 Bill
2 Gust of Wind
3 Professor Oak
4 Plus Power
3 Computer Search
2 Item Finder
2 Scoop Up
1 No Removal Gym (try to snag one or two more)

Energy

The three Grass Energy really aren't going to help you most of the time- only in very precise situations will it give you a minor edge. Let's drop those and a Psychic Energy. Here's your finished deck:
Pokemon (20)
4 Gengar 
3 Haunter
3 Gastly(fossil alot better)
2 Mr.Mime 
2 Scyther 
3 Promo Mewtwo
3 Ditto

Trainers (21)
4 Bill
2 Gust of Wind
3 Professor Oak
4 Plus Power
3 Computer Search
2 Item Finder
2 Scoop Up
1 No Removal Gym

Energy (19)
4 Double Colorless
15 Psychic
Hope that helps ya, and good luck!

~ Souper ~