The Supreme Lich
The Supreme Lich is a peerless boss like you can fight inside the Labyrinth in Deadvales. To fight the boss you must find the Summoning wand. It can be found on the Eurynomos Daemon that wanders the labyrinth.
Once you have the wand you will need to head to the large building on the south at the end of the Labyrinth and use your wand here to open the gate leading to the boss.
You will have approx 1 hour to defeat the boss. Upon defeating the boss you and the boss will be teleported back to deadvales in the building you summoned the gate on the 2nd floor.
A more in-depth wiki will be added at a later date.