Rarity

Scroll rarity
Scrolls in the game are one of three rarity types: common, uncommon and rare. Common scrolls appear in the game most often, uncommon scrolls are seen less frequently and rare scrolls are rare as the name implies. Overall, the rarity of a scroll determines how powerful that scroll is, with rare scrolls being the most powerful scrolls and common scrolls being the least powerful. When buying, selling or trading scrolls, the rarer a scroll is the more value it has.

Rarity when buying new scrolls
When buying a new scroll, the probability split among random cards is 70%, 20%, 10% for common, uncommon and rare scrolls, respectively. So there's a 10% change you get a rare scroll when you buy a random one. When you buy a pack of 10 scrolls, the pack contains exactly 7 commons, 2 uncommons and 1 rare scroll. This means that at this time there's no statistical difference between buying ten separate random scrolls for 100 gold each or buying a pack with 10 scrolls for 1000 gold. Of course, you may get lucky when buying separate scrolls and end up with more rares than you would have when buying packs. On the other hand, you have the same chance to luck out and get no rares at all.

Recognizing scroll rarity
The rarity of the cards can be identified by the markings around the border of the cards. You can also tell the rarity of your cards by selecting "Sell" in the store. The more rare the card the more used it will look.