Man, I love a good villians who waits til the right moment to attack. One of my favorite examples is from when I ran the caves of carnage. Two waves of orcs, half the party is down and this remaining are low on HP, the. The cultists attack. One PC truly died, and the only reason it wasn't a TPK was one player's ingenuity. Motherfucker saved everyone, it was beautiful and his reward was a SUPER cursed sword. This scenario really reminds me of that.
I think the term turn is confusing here. I assume you mean dungeon turn (10 minutes), not necessarily everytime a player does something. Since dungeon turns aren't really used in Mork Borg I think if that is the one intent, then some additional clarification is warranted.
I'm not a fan of traps that are save or bad thing, unless they have been adequately suggested. The trap in the refuse around the sword is pretty easy. It makes sense that putting some emphasis on the refuse might create reasonable suspicion. The traps related to the stairs not so much. I'm not sure off the top of my head I might suggest them. Maybe telling the characters at the beginning that the Were-Moose is known for being cunning and crafty or something.
The imagery of the Were-Moose coming up the stairs dragging an armoured corpse (clank, clank, clank) behind it, then casting its shadow across a party that is fighting over scraps of food and strips of cloth to maintain warmth is scary as heck. The Thing vibes for sure.