So it’s of note that as Krok is a part of the Militant Monoform Movement, he wasn’t constructed without an alt-mode or anything, but rather chose to become a monoformer by having his T-cog removed some point.
We’ve not seen what he originally was before removing his t-cog in-comics, but it is worth noting that the most recent toy released of him does have an alt-mode:
Which raises the question of if that was his alt-mode in the idw verse too.
If so, that could provide further explanation as to why he joined the MMM.
We’ve seen that having a beast-mode isn’t going to get you treated well in cybertronian society, with that being such an issue that even well respected individuals Dominus Ambus went to lengths to disguise having one.
But, if that is the case it would also make the revelation to them of what Demus was doing when Krok and the Scavengers approached him for work even more...well...