The Thief Mundus Stone in ESO (Elder Scrolls Online) is one of thirteen Mundus Stones that can be found in Tamriel.
The Thief Mundus Stone gives the player a permanent buff. The buff is visible on the characters stat sheet under “Active Buffs”. You can change your Mundus Stone whenever you want, all you have to do is find a Mundus Stone and activate it. Therefore you don’t need to worry about picking the wrong Mundus Stone because it can be changed at any time.