Apparently this is already in-stock at the American Kmart online store, so unless it is a store exclusive or is wrongly listed as being in-stock, this one really snuck out under our noses... well, for those who keep track of the gimmick toys. (and those who are looking out for more RID toys than the handful of 1-steps and Tiny Titans)

Thunderhoof as a 3-step toy.... but looks like it has the same engineering as the 1-step toy.

It's so new that the scanning code on the toy doesn't even register as being an active code on the RID game App (which they promised would be getting monthly updates... but haven't).

So I think this could be Wave 6....
Wave 1 - Bumblebee & Grimlock
Wave 2 - Optimus
Wave 3 - Steeljaw (out in America about 6 weeks ago)
Wave 4 - Sideswipe (out in America just this week)
Wave 5 - Night Ops Bumblebee (listed at online stores but not with Thunderhoof)
Wave 6? - Thunderhoof