The achievement for the Mooshataur isn't the axe. It's the Meef Stroganof. Each of you need to eat a bowl of it to get the achievement and open the next area.
Also, you can look at the chests in the labyrinth (don't open them, just put the cursor over it) and it will tell you if it's a chest or a trapped chest. If it's not a trapped chest, look at the floor. There can be a trip-wire in front of it. If neither are present, then you cna open the chest. Otherwise you need to destroy the trip wire or loot the trapped chest and run.
@Rarniw The trophy (i.e.: the head) is for a different part of the Twilight Forest. You can use any of the trophies/heads from any of the bosses to put on the pedestal to get into the goblin stronghold to fight the Knight.
if you are ever confused on what to do in the twilight forest, hit L. that will open up your advancements and they should tell you the order of what to do in there