A Wounded Fiend (not 'friend' unless you are a truly scary creature) is
impeded by mummies, as indeed a Rook would be. Notice also that it cannot
retrace its steps because of its own ichor, and therefore, as Azgoroth once
said, 'carries within it the seeds of its own destruction'. (The endgame
where each side has one Wounded Fiend and nothing else can be quite
interesting.)
This game is tough to get used to. For a while I thought I had made a major
rules error, but in fact when a Leaf Pile engulfs, the mummy does not
appear until it moves on, and so the Leaf Pile is vulnerable to being
engulfed by an enemy Leaf Pile. If it were not so, the first player would
attack with Leaf Pile (engulfing his own Human for greater speed) and win
by force.