Ummmmm, you guys know Thor is a nordic god, right? Marvel didn't creat him, they borrowed him... you do know that, RIGHT?
Yes, he is, but I was trying to find readily available references. It might take some digging to find older sources. Also, considering the subject of this show, I was trying for a little humor... I guess I should keep trying...
Image searches on "Mjolnir" seem to return a hammer, or T-shapped, ax- or club-like weapon. I did find a cricket bat which bears the name "Mjolnir", and is similar to a "wooden sword", but 1) a cricket bat, being a bat, is a closer to being a club, 2) Only Casey Jones of TMNT, not Thor, would want to use this as a weapon.
So, there you go, further proof that Thor should be wielding either a hammer or something that closely resembles one.
