It has been observed that the Transformers Collectors' Club has made something of a mini-franchise out of taking old Action Master characters and giving them new life as transforming toys. Krok is certainly an example of this trend. As one of the "new" characters created for the Action Masters line back in 1990, this toy from the club is Krok's first transforming toy ever.
When trying to figure out what mold to use for a character that's never had a vehicle mode before, it might be argued that Fun Publication's job is made somewhat easier, since they can do pretty much anything. That said, using the Stealth Bomber Megatron mold from 2013's "Thrilling 30" Generations line (itself patterned from Megatron's then-recent comics appearances) was an inspired choice, echoing several design cues of the original Action Master quite well. It's entirely plausible that this could have been Krok's originally intended alternate mode all along. Fun Publications sealed the deal not only by giving the toy a new head (seen in the following image), but by repainting the Japanese Arms Micron Dai to become Gatoraider, a new form for Krok's original Action Master partner.
While Gatoraider does transform into a weapon on its own, that's not the form shown here. Rather, this demonstrates yet another Action Master homage that Fun Publications deco guy Jesse Wittenrich came up with, for which he posted visual instructions on Twitter (here and here). Just as all basic Action Master weapons could plug into a "regular" weapon to become an even larger weapon, Wittenrich figured out how to securely plug Gatoraider into the mold's "rail gun" weapon. I have kept Krok displayed this way ever since.
Krok was only made available to club members during a limited "Transformers Figure Subscription Service" which had to be purchased before the figures were even made. While this ensured that everyone who placed an order during the availability window could get figures, it also meant that no figures were available to sell at the club store afterward. If you want to get this figure at this stage, your best bet is a place like eBay.