Mysterious cards are special cards that drop before a summer or winter sale. Since 2014, these cards have usually dropped about a week before the start of the sale. The artwork on these cards feature a number from 1 to however many number of cards are in the set. One could obtain these cards from crafting a badge. These cards eventually changed into sales cards when the sale began.
List of Mysterious card sets
- Mysterious (2014)
- Mysterious (2015)
- Mysterious (2016)
- Mysterious (2017)
- Mysterious (2018)
- Mysterious (2019)