The Grim Adventures of the Kids Next Door Easter Egg - Cartoon Network Collides

Go to the part where Grim and Numbuh One use the super skeleton strike slam. After the smoke clears, pay attention to Mandy. Put that part in slow motion as kids start popping out. Some of the characters are the Powerpuff Girls, Goo and Frankie from Foster's, and NurgulJR from Billy and Mandy.