Walking Below the Floor/Ground

I have sometimes found my avatar below the floor, and thus temporarilary invisible. Can I produce this effect on purpose? You want to know why? Suppose I wear something on my head. And suppose I put on a invisible prim. Whatever is on my head is my new "avatar" - at least to the world. This would avoid the problem with seeing water and sky and problems with transparent objects when using just the invisible prim.

Does anyone have a "below the ground" animation? Or can I wear something that triggers all animations to be negative distance to the ground?

The 'vanish' animation is a below ground animation. I've found a copy in one of the freebie boxes.