I can't take credit for this, but I saw in a review somewhere someone suggested the following changes:
make the orc able to only kill a sole character in a room. that is, if blue has 2 chars, and yellow has 1 character in the room. Red comes in with an orc and can only kill yellow because he has a 'lone' character and no backup unlike blue.
the other change is something like...
make an adventurer a 'cleric', that has an ability to, for an action, banish the wraith or kill it or push it out of the room. Perhaps too, the wraith cannot enter a room with a cleric.
This could easily be achieved by putting a sticker onto an adventurer and modifying one of the adventurer cards.
the second change would continue the whole 'rock/paper/scissor' thing of cave troll, where each character would have a way to combat it. (even though the barbarian is immune to the wraith, he doesn't particularly defeat it)