Neo Genesis is the first set for which I believe there are such artificial rarity differences for valuable cards
When the video plays, you can see just how many walls and barriers Mewtwo needed to break through for their freedom
Instead, it has you choose a creature type when it enters the battlefield and makes all of your slivers and nontoken creatures that creature type
They appeared in the Team Rocket expansion set for the first time back in 2000 and are specifically tied to the nefarious villains
This 1-drop (printed as a common) aura gives +2 to power, trample, and is pretty synergetic with the deck, and when it dies, it goes back to your hand for another casting
The reason for this is that each pack type has a different set of cards, and to build a viable deck, you'll often need two of each card you want to include