After a second thought, I cannot see this as a balanced card.
If it draws from your deck, it is simply broken. It enables constant t3 immorushes; that's how good it is.
If it adds totally random cards then it is fringe unplayable. Due to the totally random cards added, only rainbow decks can benefit from this. But a rainbow deck, exactly because it being rainbow, needs a very well defined set of cards to operate. This card won't help with that. You may get lucky with a few cards, but most of the time you would be better off by playing another copy of *insert any given rainbow card here* in place of the shard.
Yeah, if it draws from deck, and the way I read it, it doesn't, it would indeed be totally broken. I'm definitely going to try it in my rainbow deck once it comes out, because it looks very promising. Even if you get 3 mediocre cards, that's still 3 cards for the price of 1, and I'm all about card advantage
Even if it doesn't turn out to be very good, it is -definitely- by far and away the most fun of the shards, since it's a different package of 3 random cards every time you play it.