I think i have come up with an effective way to use Dark Weezing in a deck. 
Although seemingly useless, when used correctly, it may destroy any deck. 
First, here's the deck:

2x Base koffing
2x TR koffing
3x Dark Weezing
3x Scyther
3x Bulbusaur
3x Venusaur
2x Jigglypuff

2x GOW
3x Boss's Way
3x Pokemon Breeder
2x Comp Search
2x Item Finder
3x Pokemon Center
3x Mr.Fuji

21x Grass Energy
3x DCE

The strategy in this deck is to load ur bench with koffings, and a bulbusaur.
 Then, evolve into D. Weezing asap, and get a breeder in ur hand to evolve
bulbusaur into venusaur.  Then begin with the mass explosions, which its
damage may vary from 20 ~ 100 damage depending on ur bench (and ur oppenents
bench).  When ur HP gets low, energy transfer all the energy to venusaur,
then use pokemon center, then energy transfer them back, all in the same
turn!!  Then continue massacering ur oppenent.  The scythers are in there for
a strong basic, and encase of a psychic menace (aka Movie Mewtwo), throw the
jiggly in.  If u have comments or suggestions, e-mail them to
chrisjs@compuserve.com

Have FUN! :)