Cleon
Legend
Now that I've seen Cleon's post regarding his recommended Duodimensional (Su) ability, it is a rather good 3rd-edition version. For what it's worth, I'd eliminate the sideways-dimension aspect.
The vast advantage with Escape Artist checks might be problematic as they will always get out of Grapples. Perhaps instead of a near infinite bonus to Escape Artist, a straightforward +20 bonus would be better.
It'd need to be higher than that since the Escape Artist check to squeeze through a 2" wide tight space is DC 80 according to the Epic Rules.
However, since giving them nigh-infinite Escape Artist has undesirable consequences, I think we'd be better just saying "it can automatically squeeze through cracks tall enough to accommodate its height" rather than giving it an Escape Artist bonus.