I was playing Scales of War (4E D&D campaign) and we went into a necromantic demiplane off the Shadowfell. I was and am playing a half-orc monk. Well, when we came close to our destination, we encountered a woman who seemed fearful. Our wizard, who always had an itchy trigger finger and who was understandably suspicious of any living person showing up in a necromantic demiplane, immediately used a powerful fire spell (I want to say fireball, but I can't quite remember). Turns out the woman was a dryad, and it wasn't until halfway through the fight that the DM told us she was a lich.
Dryads have an annoying ability where they can teleport through trees. This was getting out of hand, as she restrained us often. So I did something I've never done before in that campaign: I tried to grab her and rolled a natural 20. I was happy that I grabbed her, but somewhat annoyed that I got a natural 20 on a grab check as opposed to, say, an attack.
Anyway, I felt pretty sure I had her where I wanted her. She felt differently. She glared at me and flung me, using her MIND, 25 feet away from her. I landed hard on the ground near a tree, which suddenly started trying to beat me up. This was the first time I've been hit so hard with an attack against my Will defense, since I make it a point to keep my Will defense high. The attack dealt 5d12+some odd damage, and it hurt. And it was hilarious. I can honestly say that that was the most fun I've ever had getting my mental ass handed to me.