The one I came up with was Schrodinger's Spellbook.
When you open Schrodinger's Spellbook, roll a d100. On a 01, it's blank. On any other result, it contains one randomly generated spell.
Schrodinger's Spellbook contains one spell.
Schrodinger's Spellbook contains every spell ever cast.
Schrodinger's Spellbook contains no spells.
All at once, until you open it up and the wave form collapses.
And of course, on a less lofty plane there are items like the red rubber fireball, the fire bucket of endless water, the red leather teddy of distraction, etc.