Imaginext Blind Bagged Series 4 is reportedly being found now at retail locations like Meijers in the Midwest U.S. of A. (according to lok of That Figures) and the number codes embossed on the top right corner on the back of their packages have been deciphered:
70 - Boxer
71 - Snowboarder
72 - Witch
77 - Space Gorilla
79 - Evil Robot
80 - Clown
81 - Basketball player
82 - Mad Scientist
I know in the past people have claimed to have found different codes in different shipments, so that may explain the gap in the numbering seen in this list here. As always, I recommend you squeeze the packages to be doubly certain you are getting the figure you are seeking.
Personally I will be all over that crazy Arkham City Joker Goon-esque clown, and that Space Ape is an absolute must have as well!
Happy Hunting, and thanks again to lok and That Figures for the heads-up!