i was at my local target a few days ago and saw a ninja bat with a green backer card instead of the usual red card. has anyone else seen any of these? or is it just a factory error?

Nope, that is a packing variation. S6 has tons of variants, one of the other boards has a pretty complete list of them, but I don't remember which one it was.

darn, i was hoping it was some rare find:D