Part of this is just personal preference (I love green-blue goodstuff) and part of it is knowing that many people default to heavy red or Monored when they dont know a cube
It wouldnt be much fun, for instance, if theres one group of characters who always win in fights
Its worth noting that both Quicksilver Amulet does this without the Creature type restriction, and Dragon Arch does it for cheaper, but only for multicolored Creatures
Reki, the History of Kamigawa Reki, the History of Kamigawa rewards you with card draw just for casting your best cards
Printed proxies are for casual play and playtesting where your pod, store, or event explicitly allows them
Three generic, Tap, Sacrifice another creature: Draw cards equal to the sacrificed creature's toughness, then discard cards equal to its power