Dagger of Everchanging Blades (2.5e Equipment)
From D&D Wiki
Dagger of Ever-changing Blades
It looks like a ordinary wooden stick about 6 inches long. At will it to be a Dagger of Venom +1, a Long sword +2, a Short sword +1, or a Two-Handed Sword +2. It only works 4 days out of the week. It can change back to look like a wooden stick at will.