So I've been looking online to see if anyone has created a canon/non canon listing of gash bell episodes, so here they are on my very own page:
Filler episodes for Zatch Bell/Gash bell:
Once you reach the end of episode 138, read volume 22, chapter 212 to continue the story properly.
139-150 have parts in them that are canon, but they are not completely canon, they are mostly filler and the manga is better.
I hope this helps
- Konjiki Gash Bell/ Zatch Bell filler episodes