Attacks - They have two attacks. One is that they will stop and shoot fireballs in 4 directions. One will be aimed at the position you were in when he started the attack, so be sure to move. The other "attack" is one where he seems to heals other chess pieces around him.
Dangers - The biggest danger is on harder modes where the Bishop will heal other pieces. This doesn't matter so much on earlier modes, but it does on later ones.
Weaknesses - Besides their fireball attack, they can't defend themselves in any other way. So once they do that attack, they're open for an attack of your own.
DMD Notes If they DT they will become a problem if they start healing other pieces, including themself.