This wouldn't be the first time we learn of cards from DotP early and I will agree that as a mythic it is pretty weak. As a rare it would have been fine, but the other card found from DotP helps a little bit with the demon. It has pretty neat flavor in that their are always groups of humans always trying to summon demons by killing themselves.
Creature-Human Cleric
A deck can have any number of cards named Shadowborn Apostle.
, sacrifice six creatures named Shadowborn Apostle: Search your library for a demon creature and put it onto the battlefield. Then shuffle your library.
1/1
Here is another one that was found.
Staff of the Wild Magus
Artifact
Whenever you cast a green spell or a Forest enters the battlefield under your control you may gain 1 life.
At the very least it isn't those other core set cards, but it still sucks incredibly hard core. Just another case of Wizards making a core set card that people will learn not to play with.
---------- Post added 2013-03-22 at 06:41 PM ----------
To do something like that would be a ton of work and Wizards wouldn't really know what to do with the cards they are sent as they couldn't resell them. Plus things like condition would be a factor and Wizards would have to possibly ship back whole sets back to the person if a few cards got damaged or were previously damaged or if the person thought they shipped every card, but forgot one or even more cards, which would cause even more hassles. If Gamekeeper or Wizards stores were still open then there would be a place for it, but unfortunately that would be too much now.