Mostly you just have to avoid copyrighted terms and unique features.

For instance... Godzilla is just a monster, but what makes him unique is his 45 degree back.

They even made fun of this issue in Dorkness Rising when they pulled stuff from the previous (apparently multidimensional) party's treasure chest;

DM: "You have a light saber?"

Player: "Of course not! That would be copyright infringement. Its a psychic sword."

A staff with a hilt otta do the trick, these things are unpainted after all.