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.