You can apply the Master Key of Thievery to an iron chain you are shackled to, which unlocks it and unpunishes you. Possibly, if your god is smiting you while you have the Key, they will avoid choosing punishment since you can easily escape from it.
Artifact lock pick Doorbane, which mostly works like a regular one but prevents doors from resisting when it’s carried.
This functionality should also probability extend to the Master Key of Thievery.
Change the Master Key of Thievery’s invoke power, since it already gives you guaranteed untrapping passively. The new invoke power is to magic map a moderate radius around you (maybe 10) and then teleport you (which will be controlled because the Key gives you teleport control), but you must pick a space within the mapped radius to teleport to.
The Master Key of Thievery can be used to lock and unlock iron safes despite them not having a keyhole.
While you are carrying the Master Key of Thievery, all door and container traps that you would have triggered are automatically removed without any triggers and probably not even any message indicating a trap was disarmed. If you actually want to trigger these traps for some reason, you can drop the Key or put it in a bag.
Possibly, these effects are suppressed when the Key is cursed (for rogues) or non-blessed (for non-rogues).
The bearer of the Master Key of Thievery cannot be seen with infravision while they carry it. (This is more useful in variants where monsters use infravision to spot the player).
Convert the Master Key of Thievery’s base item type to a lockpick. Because flavor-wise, giving Rogues a key means they never have to pick locks again.
The Magic Mirror and Master Key’s rumor-granting effects are removed or replaced, because they’re stupid and a way to read the whole rumors file while still technically sticking to unspoiled behavior.
The Master Key of Thievery can be wielded and makes 3-4 stealing attempts per hit. Alternatively, it can be wielded in the offhand while twoweaponing and make 1-2 stealing attempts per hit.
