I have a few mirror/reverse holo cards from Starter Set V too, but I have no idea where they come from. When it was first released, a few sellers were selling the non-mirror and mirror version of any given card that was not holo. A few of the cards are known to be mirror/reverse according to Bulbapedia and from deck openings on YouTube. However, I cannot find any info about the cards like Krabby.
The OP of the below thread asked the same question: