I've revised my SER deck to include current cards (and my other 2 
Mewtwos).  This deck works even better than before; even if put into 15-3C 
mode, the Slowpokes can get around the 15 trainer limit by repeatedly 
bringing back the same cards, and in non 15-3C mode, it just plain rocks.  I 
know last time I posted this deck, you suggested to chuck the Aeros, but I've 
found enough reason to keep 'em in: Wigglytuff and Clefable.  My friend has a 
really good all-colorless deck that features nothing but "pink" pokemon.  And 
lemme tell you, these pokies aren't pansies..  His deck anihilates psychic 
decks, and almost all other decks have their fair share of problems, since 
he's got 4 ER and 4 SER in his deck.  I've found that the best way to counter 
evolutions with low cost attacks (and all colorless pokemon) is to use Aero.  
Come to think, I could never rea! ! lly handle Chansey until I put Aero in the 
deck.  Anyway, enough babbling; on to my deck. 

Pokemon: 12 
3 MP Mewtwo 
3 Gastly 
2 Chansey 
2 Slowpoke 
2 Aerodactyl 

Trainers: 28 
4 SER 
3 ER 
3 Scoop 
3 CPU Search 
3 GoW 
2 Oak 
2 Misty's Wrath 
2 Item Finder 
2 NGR 
2 Mysterious Fossil 
1 Rocket's Minefield Gym 
1 Gambler (I think I'm taking this out) 

Energy: 20 
16 Psy 
4 DCE 

The whole point of this deck is to get a Mewtwo out and blast at your 
opponent's energy while beefing up Mewtwo.  The traditional response to my 
deck is "too little energy" or "too few pokemon."  I'll tell you now, neither 
of these statements are true.  You want only these pokemon in your deck 
because only these are vital to it's purpose: Mewtwo (laying the Smackdown), 
Chansey (a wall and a bomb against those colorless pokes), Gastly (for 
energy retrieval, although he is really only necessary if it comes to a late 
game), Aerodactyl (to keep pokemon from evolving and to clobber those Wigglys 
and Fables), and, finally, Slowpoke (to retrieve those wonderful trainers).  
Any other pokemon in this deck could be a potential hindrance (except, 
perhaps, scyther).  And since you need so few energy to run all of these 
pokemon on, you really don't need much of it.  The Gym serves two purposes--to 
keep all those evolving basics in the gutter as far as HP, and to eliminate 
any Gym particularly threatening at the time. 
This could be relatively easy to transfer into 15-3C; I could dump most of 
the copies of the trainers (except for copies of ER, SER, and Misty's Wrath 
or Oak) and beef up the pokecount to 3 Chansey, 3 Slowpoke, 3 Gastly and 
mebbe 3 Scyther or 3doduo/3dodrio. 
Anywho, tell me what you think.  Thanks!! ^_^   
A deck with this much explanation just screams "pick me!" It shows effort and that the person put some thought in the deck. It looks pretty well rounded, but the big problem I see is lack of attack power. Mewtwo's great, but Slowpoke and Gastly can't hold their own against most of the commonly used attackers. Chansey can stall for awhile, but if you can't get out a mewtwo, which only make up 5% of the total deck, you're going to have problems attacking.

Something's gotta give here, and Gastly or Slowpoke would be good choices. They're both weak, and have expensive and conditional attacks. Either could be replaced with Trainers as well, so I think that both could be dropped except in prop15 situations. Take out both groups and add three Scyther. Since Aerodactyl covers Evolutions, A couple Erika's Dratini would be nice to help against BBPs. I'd add another Aerodactyl as well.

To cover for Energy and Trainer recovery lost by taking out Slowpoke and Gastly you should add some IFs and Energy Retrievals or NGR, which you've already done. Misty's Wrath is contraversial; some people like it, some people don't. In prop15 it could work, but for standard play I'd take it out for two more Oaks. Add two more Fossils for Aerodactyl and yes, take out the Gambler. Also, drop the Rocket's Minefield Gym for three Narrow Gym- these'll help counter those Wigglytuffs and No Removal Gyms, and can act as a Scoop Up if your bench is full. Now we have a few too many Trainers. A few of these will have to go, I'd say one SER and the two NGR (if you find yourself decking out a lot you can always stick a couple back in.)

With Mewtwo's Energy Absorption and everyone else's relatively cheap attacks, you should be okay with dropping one Psychic to get back to 60 cards. If you run into a lot of problems with decking or too little Energy, like I said before, you can always stick a couple NGR back in. Here's the finished deck:
Pok閙on (13) 
3 MP Mewtwo 
3 Scyther
2 Chansey 
2 Erika's Dratini
3 Aerodactyl 

Trainers (28) 
3 SER 
3 ER 
3 Scoop Up
3 CPU Search 
3 GoW 
4 Oak
2 Item Finder 
4 Mysterious Fossil 
3 Narrow Gym

Energy (19)
15 Psy 
4 DCE 
Hope that helps you, and good luck!

~ Souper ~