Beholder

The Beholder is a giant floating orb of leathery flesh with one large eye in the center, smaller eye stalks on the sides, and a large mouth filled with sharp teeth.

Encounters
The Beholder can be a wandering monster on all levels of the dungeon. If you say the command "listen" before entering a room with a beholder, you will hear "magical energy."

Strategy
The Beholder is an advanced opponent in battle. It can cast spells, has many hit points, and can do a lot of damage. The beholder is one of the only monsters that has more than 100 HP, and can regenerate hit points(D10x2).