Backwards key

A crooked brass key with its teeth cut on the wrong side. Its shaft twists into a spiral, making it seem useless for ordinary locks.

Unlikely Fit. When you make a Dexterity check using Thieves’ Tools to open a nonmagical lock, you can use the key after rolling the d20 but before learning whether you succeed. Roll 1d6 and add the result to your check. If this is the first use of the key and the check succeeds by 5 or more, the key remains intact for one additional use; it breaks after that second use regardless of the result. Otherwise, it bends into useless scrap after the check. The key doesn’t bypass the need for Thieves’ Tools or grant proficiency.

Nonmagical Preparation. The key is nonmagical. If created by The Bagman's Bag, it disappears after use or at the end of your next Long Rest, whichever occurs first.