Neo: Slowking was pretty degenerate in any deck. Sneasel was degenerate by himself; it could deal up to 140 damage every turn from Turn 2 on (though that would require a lot of coin flipping; it was still a very serious number). These two became the first cards to be banned in Pokémon.
The Exes from the first Nintendo set, Ruby/Sapphire, were all souped-up versions of each type's best Big Basic Pokémon (BBP was slang back then; dunno if it still is). I always found it funny that Sneasel-Ex was actually a powered-
down version of the original
Sneasel Ex - Neo Genesis Sneasel
Hitmonchan Ex - Base Set Hitmonchan, a key part of Haymaker
Magmar Ex - Fossil Magmar, not amazing but the best basic Fire guy they could find.
Scyther Ex - Jungle Scyther, another major part of Haymaker
Electabuzz Ex - Base Set Electabuzz, the third must-have BBP from Haymaker.
Mewtwo Ex - Movie Promo Mewtwo, all aggressive psychic decks sucked without him.
Lapras Ex - Fossil Lapras; like Magmar, there really wasn't anything else.
Chansey Ex - Base Set Chansey, with an altered "heal" move less likely to create as many Stall decks with old army buddy Base Set Alakazam.