Scenario: a barbarian gets engulfed by a Mud Man. His party mates want to kill the mud man. If they attack the mud man, does the barbarian take damage?
How about various permutations on this -- does a slashing weapon penetrate the mud better than a bludgeoning weapon? How about a Scorching Ray or Fireball?
I'm also surprised that this ability doesn't seem to allow the engulfed creature to make any kind of escape attempt.
