Any card that ramps for two and costs two is a big deal and with little effort Priest is about that
Only 4 of these cards have ever been confirmed to exist, making it one of the most sought-after cards of all time
Wee Dragonauts and Nivix Cyclops have both seen play in Kiln Fiend style decks, the archetype is a little narrow for the cube because you never want these cards in any other deck
While mana is sometimes directly converted into cards, by way of plays like Divination (which converts three mana and a card into two cards), more commonly, mana is traded for influence over card quality
As the site points out, that means youd need to open something like 35 booster boxes of packs before youd likely find only one of either the Mega Lucario or Mega Gardevoir etched foil cards
For example, Kaheera, the Orphanguard's restriction is that all creatures in the deck must be either a Cat, Elemental, Nightmare, Dinosaur, or Beast card