Cow and Chicken (1997)

Season 4: Episode 19

Red Guy pops by Cow and Chicken's house selling ""invisible sauce"". Cow unwittingly buys it, and claims she's invisible, so she runs around town performing feats of ""invisibiltiness"". Red Guy sees this, and has Cow steal ""withdrawl slips"" from the bank with her ""invisibleness"". Cow steal fill-out forms instead of cash. Cow then tries to help lousy golfers, but she realizes she never was really invisible at all.