One of the most underrated cards, in my opinion, is Pidgeot.  I've even built
a deck around this guy, much to the annoyance of my opponents.  I am
surprised at how few people even deign to comment on THE most useful card in
the Jungle set. 

One of the ways you can win is if your opponent has no more pokemon to
replace any that are KO'ed or otherwise taken out of the game.  Pidgeot does
this in one hit with Hurricane.  Use a breeder to evolve pidgey into Pidgeot
and then use it's power to blow Built Up Pokemon back into his hand.

Blow away the most important pokemon on your opponent's bench, e.g., that
Blastoise or Venusaur that he depends on to feed energies to his Gyarados or
Charizard(Then blow away Charizard.)  Retreat Pidgeot and tear the helpless
basic forms apart with your stronger pokes.  This will have a bigger morale
impact than not letting them evolve in the first place.  Let them count on
the big ones and then take them away.

Or, get a few fully ready Pidgeots and blow away his entire bench for a real
easy win.
The only serious threat I can think of is Haymaker, with it's thunderpunchin'
Electabuzz.  Don't use this deck against Haymaker unless you have Hitmonchan,
or something.

Vegita
email @ scipiodxxi