Rainbow Cap Switch

The Rainbow Cap Switch is an anomalous cap switch similar in nature to the Yellow Cap Switch. It is reported to be found in secret levels added by the Personalization A.I. or in place of other cap switches, most commonly replacing the Metal Cap, or the Wing Cap in a copy affected by the Castle Living Space Anomaly. The Rainbow Cap Switch is reported to usually be found as a "final power-up".

When the switch is activated, reports of what it unlocks are inconsistent. Some reports claim it unlocks new movement options, such as a Triple Jump. In some cases, however, it will instead unlock a new Cap. This Cap may either be a replacement/upgrade for the Metal Cap, or be an entirely new one. This new Cap is usually referred to as the "Rainbow Cap", and is referred to by some players as the "Starman", based on the power-up seen in many other Mario titles.

The Rainbow Cap
The Rainbow Cap is reported to act similarly to the Metal Cap and Koopa shell, most commonly giving the player invincibility and the ability to run through enemies and breakable objects to destroy them. They also usually allow the player to walk underwater, albeit without the jump height decrease or other weight-based effects of the Metal Cap. The Rainbow Cap is occasionally reported to be somewhat unstable, sometimes causing the game to crash.

Unlocking the Rainbow Cap
The Rainbow Cap is commonly unlocked as the last Cap Switch the player can find, usually in an anomalous area such as the Fourth Floor, although in many cases it has also been reported to out-right replace the Metal Cap Switch.

In copies where it is it's own unique unlockable however, reports of unlocking it are relatively consistent among players. The usual report of finding the Rainbow Cap is that it appears in a secret sub-area of a sky-themed level, usually Rainbow Ride, or anomalous stages such as Starlight Skyrise. These secret areas are commonly space-themed, and are usually found in high altitudes of the main stage.

The Rainbow Cap is strangely reported to only appear to more experienced players. This seems paradoxical, as due to it's nature of granting the player invincibilty, it would seemingly make sense to provide it to less experienced players who might be struggling. This is believed to be done by the A.I as a method of "rewarding" players for overcoming it's tougher challenges, with a shiny rainbow-themed unlock.

The Rainbow Cap in Action
The Rainbow Cap appears in several courses in copies that feature it. Common uses of the Rainbow Cap include making use of it's invincibility to cross hazards, destroy otherwise impossible to break objects, or simply run through a large cluster of enemies. It also has a use in some Missions due to it occasionally granting the player a speed or jump boost, allowing them to complete objectives or make gaps they otherwise wouldn't be able to.

Strangely, the Rainbow Cap may appear in the Castle itself, most often on the second floor. The reasoning behind this is unknown, and to date no uses for the Rainbow Cap in the Castle have been found.

Theorizing
It is believed that the Starman was scrapped due to the potental of players confusing it with the Power Stars, due to the Starman Power-up often being found by collecting yellow stars in other Mario games. It is then believed that assets or code relating to it was left in the games files, before being subsequently used by the A.I, commonly dubbing it as the "Rainbow Cap".

The Cap commonly appearing in space-themed areas is believed to be related to an original, scrapped method of obtaining the Cap, related to the Mario Kart stage "Rainbow Road", due to them sharing a theme of rainbows in space. The A.I may be picking up on this unfinished or scrapped code and re-implementing it in some capacity.