You could have gotten it from the MechQuest Art Book, but HeroMart no longer sells that so you can't get the code anymore.
you must type skull-??????-crusher
mundu
redblueblackwhite
OICU812
you simply go on a server and say /enter skull code
you just type in a random code
The code is in the art book that you order at the MechQuest homepage.
art5-6274-6030-1524
o81
You get the skull crusher hammer when you beat phantom ganon at the forsaken fortress
The skull crusher exercise targets the triceps muscles in the arms.
I don't know that's what im trying to find out