Unless I'm missing something, Frost 12 does no longer seem to be solvable in the Holiday Lemmings Neo player (tested on v1.36).
You only have 2 bashers, one of which is needed to break through the steel "box" and one to free the path to the exit. So once you left the "box", you have to make sure to have a Lemming facing right do the dig down. This is perfectly possible in the Traditional version (successfully tested on V29), as the Lemmings turn around when they hit the ceiling at the hilltop. In the Neo version, they just keep on walking left, and you have no spare skills to do anything against it.
It does indeed seem to be impossible. Thanks for letting me know, I'll fix that in V1.36n-B. :)
I have actually managed to solve the unfixed version of Frost 12. :D :-[ Just a bit of release-rate tweaking and more importantly, a bit of luck and determination to get the right-facing digger in the right place.
Still, the new mechanics made the position of this level unfavourable. Maybe we should move this to Hail 16? :P