This question reminds me of an issue I was wondering when play with the bard 1-3 preview . . . how do misdirected mark and vicious mockery compare to each other?
Misdirected mark deals 1d8 damage over vicious mockery's 1d6, but vicious mockery is against Will; that seems to even out.
Now, vicious mockery gives a -2 penalty to the attacks against anyone, while misdirected mark gives the penalty to everyone except one of your allies. So I guess it kind of motivates the monster to attack one ally . . . but apart from having a fighter or warden to have the mark 'come from', these marks don't really work well with other defender classes (paladin or swordmage, and potentially future defenders).
Overall, I think I have to favor vicious mockery, but I guess having a fighter or warden around could change that.
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I think the idea with Misdirected Mark is that you mark the enemy to a target they can't easily reach - So if a monster is locked in Melee with a Defender and a Melee Striker, you connect his mark with the Wizard who is 10 squares away. When used well, it basically gives the enemy the same -2 to hit as Vicious Mockery, since they can't readily attack the target they're marked by.