Force marbles creates a layer of invisible spheres of force about one inch in diameter, spaced about one inch apart, which can cover any surface (walls, ceilings, doors, mud, water, snow, quicksand, and so forth). The spheres are fixed, but will spin in place if anything pushes on them, such that any creature on the surface when the spell is cast or moving across it while the spell is in effect must make a successful Reflex save or fall prone, taking 1d6 points of nonlethal damage. This save is repeated on your turn on each round that any creatures remain within the area.

A creature can move over the surface at one-half normal speed with a DC 10 Acrobatics check, with failure indicating it can’t move that round (and must then make a Reflex save or fall), while failure by 5 or more means it falls. Alternatively, the layer of spheres adds a +15 circumstance bonus to the Climb DC of any vertical surface.

The immobile spheres form a barrier of sorts over any surface they cover. The layer itself has a hardness of 10, 25 hit points per 5-foot section, and a break DC of 20. If the layer rests on a solid surface, add the hardness of the force marbles and the surface together, then divide any damage that gets through the combined hardness between both surface and layer (with the layer taking any odd points of damage). If the layer runs out of hit points before the surface does, the surface no longer benefits from the layer’s hardness. If the surface runs out of hit points before the layer does, a section of the layer is destroyed along with the surface. Likewise, when the layer lies on a solid surface, add one-half the lower break DC to the higher break DC. Breaking the layer and the surface destroys them both.

You can shape this spell’s effect to cover any four 5-foot squares on a surface, so long as the squares are contiguous. If you attempt to cast the spell into air or empty space, the layer collapses and the spell is wasted.