Gofu (護符), also called ofuda (お札 or 御札), is a type of Japanese amulet or talisman traditionally made of a strip of paper.
In TMNT #132, Oroku Saki instructs the Turtles to create their own gofu using elements found within the thin place's mystic forest. He tells them that they must reflect their true selves so that they can tether to their spirits. Rather than paper, the Turtles gather natural items - crystals, mud, twigs, plants - and in Jennika's case, some sort of bird skull - to construct their amulets. After completing a ritual, the amulets mold into green crystalline forms.