Grim Adventures of Billy and Mandy, The
Cartoon Series: Season 02; Episode #08: "Terror of the Black Night/Battle of the Bands/Halls of Time" (August 01, 2003)
Grim, Mandy, Billy and their friend, all visit father time. Billy and the friend find everyone's personal hourglasses. They first mix the friend's brother's hourglass which causes him to turn into a baby and then an old man all while he's trying to hit on a girl. They are then kicked out of Father Times place for trying to steal everyone's hourglasses. On the way back everyone stars getting younger. This is due to the fact that Billy and his friend left the hourglasses upside down, thus causing their time to go in reverse. They try to get back in time, but one by one they each are regressed past the point of birth. They are ARed out of their clothes, but it's not all that neat seeing as how they were kids to begin with and Grim is just a skeleton getting smaller and smaller.
Grim Adventures of Billy and Mandy
Cartoon TV Series: Season 02; Episode #09: "Grim for a day" (Friday August 15, 2003)
When Billy and Grim get into an argument over who has it harder, Mandy suggest they switch places for a day. However, they soon regret it, as they find themselves transforming into each other. (ST)