Like Darkwing Duck, Negaduck doesn't wear pants, but when he takes off his Darkwing disguise, he was wearing underwear. Then when he puts on his yellow costume, they were gone.
When Darkwing Duck transforms into a baby, he was wearing his hat, even though he hadn't been wearing it since it was on a chihuahua that made Launchpad and Gosalyn thought was Darkwing transformed into a chihuahua, but when he transformed back to normal, his hat was gone.