A Brief Explanation of Rarity

Rarity breakdowns tell you how many of each card exist on a press sheet. The lower the number, the rarer the card. Press sheets generally contain 100 cards. Each sheet represents a card rarity (Common, Uncommon, or Rare). A certain number of each card is printed on its corresponding rarity sheet. Thus, an R2 card appears twice on 1 Rare sheet.

The Common cards for Rifts are slightly different due to the collation. Using the cards laballed as C2 as having a base rarity of 2, the cards labelled C3 have an effective rarity of 2.25, and the cards labelled C4 have an effective rarity of 3. Since you made it this far, I'll also tell you that one Common has an effective rarity of 1.5, but I won't tell you which card it is...