The items obtained from the other four slots in a pack can be a Mercenary Card, Coins, or Portraits, from which you may obtain Mercenary Portraits of Mercenaries that you own before owning all Mercenary Cards of the rarity.
why would anyone think after getting 1 mercenary in a pack that there is 0 chances of getting a portrait from a rarity you still dont own all mercenaries of…they literaly tell you it can happen !