[ericthered]

The steel wall bubbles and expands, shifting into an enourmous amorphous mass of hard, psuedo-durable construction foam.

The guy with the missile launcher fires away blindly as the wall reaches out to him. The foam itself won't be slowed, but the splatter that gets through could harm Halcyone...

Halcyone is a random distance between 1 and 10 yards from the attacked wall.... and the distance is 5. The actual attack roll of the weapon does matter, I suppose... its a solid hit. with 27x7(10), damage, the explosion can get through as well.

The fragmentation damage scores a single possible hit, doing 7 cutting damage. The target is the left arm.

The shooter shot from WAY too close, and they're quite a bit singed. A helmet deflects one chunk of flying metal, and a smaller one cuts through the body armor, dropping him.

Is the wall on the side with a single immortal going to expand as well, or remain metal?

The wall advances at 1 yard per second. It gently pushes most people: anyone truly determined might be able to stand their ground, wave their arms, and make a little bubble for themselves...