I imagine Yurgir is the one who broke through the wall in grymforge, which is seen in the scene with stonemason Kith.
That scene left me expecting something larger than Yurgir.
*
I would also add that Yurgir and the meregons should be a lot more powerful considering they took out the entirety of Grymforge when they attacked. This was the army that defeated Ketheric Thorm. Even if this is the remnants of that army, it leaves me thinking Ketheric's forces must have been pretty weak.
