I only ever collected Gen 1 and a handful of Gen 2, but I played the game a lot back then and still have my cards. (I should play it again sometime soon...) My most prized cards, as well as probably my rarest and my most powerful are my Dark Machoke and Dark Machamp. I think they're from the Team Rocket set.
Dark Machoke has two attacks, Knock Back and Drag Off. They both mess around with the other player's active Pokemon and bench. Knock back damages the current active Pokemon and forces him to switch with another, whereas Drag Off does a little less damage but allows you to choose the new active Pokemon out of their bench and actually attack it.
Dark Machamp was much simpler, but even more brutal. Fling allowed him to take the active Pokemon and shuffle it and all attached cards into the opponent's deck. Then he just had Mega Punch which did 40 damage.
With these two I could endlessly screw around with my opponent's bench and completely control the game as long as I kept them alive. I was also a fan of Elekid, because his Pokemon Power allowed him to hit Pokemon while he was still on the bench. Honestly not a bad combination with Dark Machoke and Machamp.
Dark Machoke has two attacks, Knock Back and Drag Off. They both mess around with the other player's active Pokemon and bench. Knock back damages the current active Pokemon and forces him to switch with another, whereas Drag Off does a little less damage but allows you to choose the new active Pokemon out of their bench and actually attack it.
Dark Machamp was much simpler, but even more brutal. Fling allowed him to take the active Pokemon and shuffle it and all attached cards into the opponent's deck. Then he just had Mega Punch which did 40 damage.
With these two I could endlessly screw around with my opponent's bench and completely control the game as long as I kept them alive. I was also a fan of Elekid, because his Pokemon Power allowed him to hit Pokemon while he was still on the bench. Honestly not a bad combination with Dark Machoke and Machamp.