Basic lands come in six types, with each of the six producing a different type of mana when tapped: Plains produce white mana, Islands produce blue, Swamps produce black, Mountains produce red, Forests produce green, and Wastes produce colourless (and are much, much less common than the other five, having only appeared in one set)
The biggest downside of the deck is the heavy reliance on your commander
Not only is this an infinite coloured mana combo, but it's also an infinite enters-the-battlefield combo
What affects the value of M Mewtwo-EX
This consistency and redundancy are its greatest strengths
This makes identification more structured, but also more complex for those unfamiliar with the system