OK,  I just thought of this combo last week, 
and if it sounds too good to be true, it just might be (I'll explain 
later).
 
===================
Scizor        
    80 HP    M
===================
[M] False Swipe (?) 
Does
damage equal to half 
the
defending Pokémon's
remaining HP (rounded
down to the nearest 
10).
 
*[3] Double Claw (20x) 
Flip
2 coins. This attack 
does
20 damage times the
number of heads.
 
Weakness: F
Resistance: Grass
Retreat Cost: 2
===================
 
*I believe Double Claw was mistranslated. The US 
card has "20+" instead of "20x," which implies that the attack SHOULD 
read:
 
Flip 2 coins. This attack does 20 damage plus 20 
damage times the number of heads.
 
However, I believe Wizards' official ruling is that 
the "20+" is the misprint, not the attack description, so I went with this one. 
(You don't need that attack for the combo anyway.)
 
===================
Porygon         40 
HP    C
===================
 
[1] Conversion I (): If 
the
Defending Pokémon has
a weakness, change 
its
weakness to any type
other than colorless.
 
[3] Psybeam (20): Flip 
a
coin. If heads, the
Defending Pokémon is
now confused.
 
Weakness: F
Resistance: P
Retreat Cost: 0
===================
 
Alright, those are the cards, here's the combo (in 
case you haven't already figured it out). Use Porygon's Conversion to change the 
Defending Pokémon's weakness to Metal, then use Scizor's False Swipe for an 
instant KO!
 
False Swipe damage = [(Defending Pkmn's HP) / 2] * 
2 (for weakness) = Defending Pkmn's HP
 
It won't work on Pokémon with an odd number of HP, 
since False Swipe rounds down, but a Plus Power easily remedies this. This also 
works with Base Set Porygon, but TR Porygon is WAY better (10 more HP and free 
retreat). Also, this will not work on 
Pokémon with no weakness. Babies, Darkness, and 
legendary birds (just to name a few) are immune to Porygon's Conversion I. So, 
it's a good idea to have other Pokémon to support this combo.
 
This strategy is mainly useful for those pesky 
Pokémon that just won't die...er, faint (Chansey, Steelix, Charizard, other 
120 HPs). Of course Metal Energies on the opponent really put a damper on this, 
but Plus Powers and ERs work in a pinch. Since no Pokémon have resistance to 
Metal, you don't have to worry about that, but you DO need to worry about Unown 
M. Gust and use another hard hitter (like MP Mewtwo or Rocket's Scyther) to KO 
that pesky Unown fast.
 
OK, I think I've gone on long enough. As you can 
see, this combo has its flaws, but it does have potential. Let me know if you 
like it or have any suggestions. No spam/flaming please.
 
BTW, this is my first submission to Pojo.com, so 
don't judge me too harshly! o^_^o Oh, and is it alright if I plug my Pokémon 
Apprentice theme? Oops, did I type that? *psst! email me if you want it! it's 
really good!*
 
Ankh-Morporkian