The cape is an item used in Back to the Freezer. It is found in the cupboard in the Hide and Seek staging area of the secret bunker on the iceberg on RuneScape Brazilian worlds. It is used to make the flax cap-ice-i-tor on those worlds, taking the role of "indispensable for all superheroes". It replaces the hat, and will transform into the hat if taken to an English world (or vice versa).
