For newer players, what that means is that if you tap a Forest for a mana you can get another Green mana, but if you tap something like a Watery Grave for a Blue mana, you can also get one Black mana for free
One of the biggest debates in the community is whether or not the Reserved List is a legally binding promise: could someone with a huge collection of old Reserved List cards sue Wizards if it started reprinting cards on the Reserved List
Thankfully, while some MTG players were upset by these decisions, the MTG Final Fantasy Holiday Release helps even out distribution
This becomes completely nullified if you need to pay mana to keep them around
But for now, I think she's too hard to play consistently and too "win more" even when you can play her
Bonus Tip: When youre building a deck for a Constructed format like Standard or Modern, as well as the 60 main deck cards, you can have an additional 15 cards in your sideboard (if you use one)