A 75

The power prevents movement by foot, but not by climb, swim, fly, or teleport speeds. (If you can fly, you can still charge.) It also doesn't trigger anything that keys off "immobilized" like World Serpent's Grasp. I'm not perfectly sure about shifting and can't find clarification anywhere but would assume that shifting also requires an alternate movement mode. Shifting does require moving ... it seems to me that not being able to walk/run prevents any kind of moving based on walking/running.

Immobilization is itself one tiny corner of 4e that's NOT crystal-clear. Some kinds of immobilization go with you when you teleport/slide and some don't. I have a rough time when I try to 'brew effects that hold creatures in some way -- many words needed.