Dark Weezing- never used and considered, well, bad.
Ditto- supposedly one of the best cards in the game.

After this analagy, who would think Dark Weezing could beat a ditto?  I
did and i'll prove it.

Dark Weezing's Mass explosion attack reads that you do 20 damage times
the total number Koffings, Weezings, and Dark Weezings in play (your's
and your opponent's).  Then, do 20 damage to each Koffing, Weezing, and
Dark Weezing in play (your's and your opponent's).  Mass explosion has a
base damage of 40 against ditto, because it counts as a dark weezing. 
Then ditto takes 20 more damage, for the same reason.  With the 60 HP of
a dark weezing, ditto is KO'ed.  You can also put a metal energy on your
D. Weezing to keep it from damaging itself.

The only hazard here is that it can work the other way around to.

SuperSpaceGuy
You can reach me at boyzbot@home.com