Thats because Reya Dawnbringer, in addition to a not too shabby 4/6 Power and Toughness (though you may be expecting more for such an expensive card), can bring one creature per turn back from your graveyard, returning it straight to your battlefield
It can also serve as a single-creature Fog, since it takes the creature attacking you out of combat because its no longer a creature
One thing I hate about this graphic is that it isnt in order, according to the box opening videos Ive watched
This means Aven Courier can copy shield counters and pass them around the field, or one of the buff counters used by Denry Klin
Mark Rosewater himself has commented that while the mechanic was beloved by many, its logistical issues made it too clunky for regular use
Snow Duals These are an awesome cycle of cards