The Prism Shield[from internal data] is an item, first appearing in Kirby's Return to Dream Land (and since appearing in Kirby's Return to Dream Land Deluxe) which creates a sustained energy shield over the head of its carrier.
The shield resembles a brass instrument, specifically a French horn, with a large blue star insignia on the central pipes. This star changes color as the Shield becomes more unstable, and flashes red when it is about to break.
The Prism Shield can be picked up, carried, and thrown like many other items in the game. Similarly, the character holding the Shield can only make one jump and cannot use any attack but a Sliding Kick. When thrown, the Shield itself can deal minor damage to enemies. The main selling point of carrying the Prism Shield is that, while held, it will continuously output a rainbow energy barrier over the head of its carrier, protecting them from any and all attacks from above, with the exception of large crushing objects. It does not protect in any other direction, so the wearer must make good use of a Sliding Kick if they wish to keep carrying the Shield in certain instances.
Kirby using a Prism Shield in Cookie Country - Stage 4
Kirby using a Prism Shield in White Wafers - Stage 4 in Kirby's Return to Dream Land Deluxe