Weapon/object duality is a game concept that is a feature, often mistaken as a glitch, in Problem Sleuth whereby all weapons have an innocuous double, switching back and forth between the two forms seemingly at random. Interestingly, the object and the weapon may have large differences in their degree of encumbrance. Bizarrely, they often do not, the hairpin being heavy enough to break the glass in the skylight. Pumpkins also seem to have this effect in Jailbreak, though their innocuous double is nothing (or air).
In Homestuck, the Midnight Crew exhibits this with their decks of cards. Every card in their deck corresponds to an object, usually (but not always) a weapon, with the deck as a whole corresponding to a storage unit that stores each individual object.
Kanaya Maryam has a Chainsaw/Lipstick, but it appears to collapse or expand mechanically from one object into the other. This oddly achieves the same effect as the duality seen in Problem Sleuth without any "glitch"/special mechanic occurring. Her chainsaw/lipstick appears to be designed to transform rather than doing so for no apparent reason such as in Problem Sleuth and the Midnight Crew's cards.