These are not blank backs.
They were on Kelloggs cereal boxes in Canada. I have six of them all from the same box panel. I also found pictures of another 5 but I have no idea how many are in the set. They are all NNO.
What I have / found so far:
Robin
Dick Grayson
Edward Nygma
The Riddler
Bruce Wayne
Two-Face
Batman
Barry Bond - Two-Face(?)
The Plan
Crimefighting
Bruno
--------
Check my Profile page to see my 2023 Goals and my Lists of sets near completion (5 cards or less) or sets getting close (less than 100 cards missing and 75% complete).
https://www.tcdb.com/Forum.cfm/Page/B/ID/0/?MODE=VIEW&ThreadID=25745&C=0