Per 
SCP-XXXX "Thief Of Thieves"
SCP-XXXX.
Item #: SCP-XXXX
Object Class: Euclid
Special Containment Procedures: SCP-XXXX is to be contained in a 2 X 2 X 2 X 2 metre containment cell at Site ██. No less than two security personnel are to guard the cell at all times ensuring SCP-XXXX does not breach containment. Video feed of SCP-XXXX is to be observed by at least two personnel at any given time. Cameras in SCP-XXXX's cell are to be re-positioned weekly to ensure SCP-XXXX does not know it's being watched, so it does not steal or tamper with the equipment. One camera is to be given to SCP-XXXX monthly in experimentation cycles. UPDATED CONTAINMENT PROCEDURES: Cameras are always to be kept away from SCP-XXXX as of Incident XXXX-01. Personnel Level 2 and under are not to interact with SCP-XXXX.
SCP-XXXX is to be "given" various objects in various amounts once every three days in the following fashion. SCP-XXXX will be escorted to a decoy cafeteria identical to the one housing SCP-294 at Site ██. Staff in the room during experimentation are to have on their person at least one easily replaceable, non-dangerous item unless explicitly instructed otherwise. SCP-XXXX is to be released in the area for fifteen minutes to fulfill its needs of stealing objects from other beings. Other objects are to be strewn around the room whilst other personnel pretend to have misplaced them. Once SCP-XXXX is done thieving or once the fifteen minute time limit has been hit, it is to be taken back to its regular containment cell immediately with normal procedures until the next cycle. When/if the objects appear again after being stolen it is required to report it to designated personnel to be documented.
Description: SCP-XXXX is a small reptilian entity, roughly 18.33 cm long and 4 cm wide, and is mainly strong cool green in colour with light cerulean spots. It has the ability to steal objects off of someone's person or take items that are laying around, and make people think they've been misplaced. Anywhere from twenty minutes to twenty days later, the object is returned in perfect condition in a place completely unrelated to where the individual "lost" it. On occasion as of ██/██/████, something new may come with the object, or the item in question may be improved. Instances of this (SCP-XXXX-1) are to be reported immediately for further testing.
SCP-XXXX has also been observed to take thoughts out of someone's mind during its experimentation cycles and plant them into another (see Addendum XXXX.3). It is unknown how exactly it does this, and further experimentation is required.
SCP-XXXX is unable to be directly observed in stealing objects as it is [REDACTED], however; the phenomenon only occurs when it is present. It is unknown where and how SCP-3684 hides these things, returns them, or what it does to them.
SCP-XXXX was previously classified as Safe and had less severe containment procedures as it only took replaceable and safe things such as watches, belts, etc. As of ██/██/████ it breached containment and began stealing items of importance, such as personnel card keys, first aid material, classified documents, weapons, and even SCPS themselves- such as SCP-1499, SCP-1025, SCP-513, and others. It was then ordered to have stricter containment procedures and classified as Euclid.
Addendum XXXX.1: As of ██/██/████, returned objects stolen by SCP-XXXX have been observed to be improved upon return on occasion. Similar to instances of SCP-914's machinery, a stolen cell phone was returned with all the same information in its system and the same serial number; however, the model was upgraded to the newest in its series. Upgraded or improved items will be studied under the name SCP-XXXX-1.
Addendum XXXX.2: INCIDENT XXXX-01: After an instance in which SCP-XXXX was given a small camera with video functions, two personnel observing the video feed were [DATA EXPUNGED] and had to be rushed to the hospital on-site. One of the two personnel was left with permanent damage to [REDACTED], and the other staff died of [REDACTED] several hours later after receiving the same treatment.
Addendum XXXX.3: Experiments have been conducted in which two D-Class personnel are placed in separate empty rooms, one of which also containing SCP-XXXX. The D-Class in SCP-XXXX's presence was ordered to focus on a very specific object, and the other D-Class was told to think of a different object, completely unrelated to the first. After about ten minutes, the thoughts from the two test subjects completely changed- the first D-Class could not recall what he was asked to think of, and the second reportedly started thinking of the first D-Class' object "out of nowhere."