In the Creature Compendium I read that:

1- Creature retreating with 2 adjacent retreat hexes blocked (1 by a Creature the other by 2 units) has to deal with:

- Critical Hit Check for the attacker. (attacker rolled 3 flags).

- Critical Hit Check for the failed Retreat (1 flag ignored, 4 hexes needed to Retreat, 4 dice are rolled, and some maybe re-rolled).

2- Creature has to Trample those units. So:

- Creature first, Critical Hit Check (4 dice rolled). If Creature dies, path is still blocked because damage needs to be dealt to the other 2 units.

- 2 units are trampled but the Creature still has 2 hexes to Retreat, due to the last of the 3 Flags rolled.

3- Creature has now an open Retreat path and needs to Retreat 2 hexes. It goes back one, and then finds itself trapped because of impassible terrain.

Q: According to the Compendium, when Retreating, if a Creature finds itself blocked by impassible terrain, the Retreat stops. Should the Creature check for Critical Hits with 1 die, in this case? And is it the same with other normal units? I thought impassible terrain always worked like blocking units, etc...

Before any trampling can occur, a critical check on the retreating creature equal to the number of hexes remaining in the creature's retreat is taken. For example, if a creature's retreat path is blocked on both hexes while three hexes remain in the creature's retreat, a 3d critical check is taken. If the check is failed, the creature is removed from the board, and nothing happens to any blocking units. If the creature passes, then the trampling begins, and no further critical checks are taken for that creature as it has already passed for the remaining hexes, regardless of if they are blocked or not.

You're right. The Critical Check was already done in the beginning, for all the hexes she couldn't Retreat at the beginning. Even if it's able to Retreat more due to Trampling, it doesn't get -1 die for the Critical Hit Check because it was resolved right in the beginning.

Thanks, my bad.

No worries - plus, I don't agree with this method of resolving the trample situations I know that a main reason it is done this way is to keep it simple and save time, but I would prefer that the critical check for the retreating creature is alternated with the figure loss/critical check of the blocking unit(s).

It isn't a situation that arises all that often though, as players who are controlling creatures learn very quickly to keep an open retreat path behind that creature, and even if they don't, takes a roll of two or more flags (or a lore play) before the situation arises.