No less than 12 level 3 personnel are to be within 50m of the object. Drawing from the emotions of those within range SCP-666 has been noted to change colors, emit frequencies of sound never before recorded by anything but man-made sound devices, and even cause apparitions to appear that are solid and capable of interacting with personnel even on a sentient level.
Of those who have come in contact with the object, the most valuable result has been an inexplicable convergence of the subjects mind and that of the skull. Vast quantities of information regarding [DATA EXPUNGED] have been revealed, and since research on SCP-1??, SCP-0??, and SCP-4?? have grown in ways never imagined before.
Addendum: Those with O4 Security Clearance should see document #666-b
Document #666-a: Recordings of contact with SCP-666
???? ??????, the first to bring the object to SCP's attention, and the first to touch the object on record has felt the following effects while under supervision;
Extreme visual and audible hallucinations relating to wars never fought in human history.
The belief that he can hear the skull speak. All statements regarding these discussions
have only lead to ways to play simple board games after extensive efforts
to translate the language spoken when inquired.
Several patches of skin affected by what seems to be a rash. No adverse affects from
the rash as of yet, though they seem to secrete massive amounts of phosphoric acid.