(defun C:POOF (/ ent) ; makes selected object invisible
  (setq ent (entget (car (entsel))))
  (if (assoc 60 ent)
    (setq ent (subst '(60 . 1) (assoc 60 ent) ent))
    (setq ent (append ent '((60 . 1)))))
  (entmod ent)
  (princ)
)

(defun C:UNPOOF (/ ss n ent) ; makes invisible objects visible
  (setq ss (ssget "x" '((60 . 1)))
        n (1- (sslength ss)))
  (while (>= n 0)
    (setq ent (entget (ssname ss n))
          ent (subst '(60 . 0) (assoc 60 ent) ent)
          n (1- n))
    (entmod ent))
  (princ)
)