supertux/data/images/objects/bonus_block/invisibleblock.sprite

(supertux-sprite
      (action
        (name "default-editor")
        (images "bonus-invisible.png"))
      (action
         (name "empty")
         (surfaces
          (surface
           (diffuse-texture (file "empty.png"))
           (displacement-texture (file "displacement.png")))))
)