While the latest article on Porygon is quite good, it's worth noting
that the Wizards of the Coast FAQ explicitly states (this is quoted
right from the FAQ):

Q: How long does Porygon's Conversion last?

A: Just while the converted Pokémon is the Active Pokémon. Remember that
anything other than damage that was the result of a Pokémon attack goes
away if the affected Pokémon goes to the Bench.

So if the converted Pokemon is retreated, switched, whirlwinded, etc.,
Porygon really doesn't do all that much.

It's an interesting card, but not an easy one to build a deck around.
You'd probably want to use it with lots of Gusts of Wind, and Gust up
the Pokemon that's least likely to retreat. You'd also want to play with
Dodrios or lots of Switches because you'll need to retreat Porygon so
frequently that it's not worth dropping the energy into the discard pile.
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Leanne Opaskar                         lopaskar@san.rr.com