a.k.a. Tasan, or "Prismatic Bomb".
A large black box with three triangles, reputedly a powerful device capable of destroying even artifacts. Don't drop it. Don't hit it. Don't cast spells at it. Really. Seriously. It's bad news.
10/2001 Note: When disturbed (as opposed to a full activation), the Tasan fires out a short-range burst of prismatic rays, as per the spell in the PHB.
12/2001 Note: The Tasan destroyed the DungeonOfThePerishingFall, as well as the artifact powering the undead, in the season finale.