When using a magic item, roll 2d6, add one half relevant class level (round up) and any item level (use enchantment bonus if it has one, or make a ruling). Then consult the table below.
|2 or less||Destroyed (item ruined, triggers chaos surge)|
|3, 4, 5||Warped (does not function, chaotic energies twist device)|
|6, 7, 8||Undermined (functions, but not quite as expected, device left unchanged)|
|9, 10, 11||Consistent (device functions without surprises)|
|12 or more||Augmented (functions, chaos embues the device with a new permanent ability)|
For example, a magic-user deploying a staff would get the class bonus, but a fighter would not. natural 2 and natural 12 should always override any modifiers, just like how nat 1 and nat 20 are often interpreted. If you wanted it to be more swingy, you could only apply item level (and ignore character level). That would also decrease the load on referee creativity (by not requiring the invention of new permanent abilities quite as frequently).
Perhaps especially useful for handling magic items in FLAILSNAILS games.
A great question from Eric B. on Google Plus: Would there be ITEMS OF CHAOS with negative item levels?
To which I responded: yeah, that sounds like a good way to operationalize curses. “Most of the time this wand will just make problems for you, but once in a blue moon it will level the evil overlord’s fortress.”