It has the least impressive final ability, but its still pretty playable
You can copy your opponents best creature, perhaps a Titan or a dragon with a powerful enter-the-battlefield effect, swing with it immediately thanks to Haste, and then still have a functional mana rock for your future turns
Most notably it was just the best end-game you could build your deck towards, but its not clear that is really the case anymore as there are cards like Nexus of Fate that can go much bigger
One mana is a steal, however, as shown by cards like Blasphemous Act
Of the game stores I visited with some regularity back then, Card Collector is the only one that still exists
I need to preface all the whining I'm about to do with this being a fantastic thing Pokemon does: no other game does it, even though they absolutely should