The Grim Adventures of Billy and Mandy - Season 6 - Eps 15: Dumb-Dumbs and Dragons
As Billy sees Hoss Delgado's manliness is action again, Billy wishes to grow up to be a hero like him. Grim tells Billy that in older times an evident way to become a hero was to slay a dragon. They travel to the Middle Ages so Billy can train under the supervision of the best dragon slayer, Sir Boss Del Guapo, who resembles the present time Delgado. Billy becomes friends with the dragon he was supposed to kill and spares his life, becoming the dragon's hero. Del Guapo finds himself transported to the present, where he has a brief encounter with Delgado.
About The Grim Adventures of Billy and Mandy

Title: The Grim Adventures of Billy and Mandy
First Air Date: 2001-08-24
Last Air Date: 2007-11-09
Status: Ended
Rating: 8.045/10 (from 958 votes)
Language: EN
Seasons: 8
Total Episodes: 184
Network: Cartoon Network
Genres: Animation, Comedy, Kids
Production Companies: Cartoon Network Studios
Synopsis
The exploits of the Grim Reaper, who has been forced into being the best friend of two children. A spin-off of the show Grim & Evil.
Cast

Greg Eagles
Grim (voice)

Richard Steven Horvitz
Billy (voice)

Grey DeLisle
Mandy (voice)

Vanessa Marshall
Irwin (voice)