Elemental Tiles
Trap
Level 16 Obstacle
XP 1400

The area is riddled with floor tiles that transform before your eyes. At times, each tile resembles stone that ripples like water; then it transforms to boiling ice. Later the tile dances with a flame-colored mist that crackles before it grows into spikes of lightning. Whatever these tiles are, they don’t look stable.

Trap: Each of these traps has eight strategically placed tiles, and whenever a creature enters a tile space, it is attacked by a random form of elemental energy. Also, when creatures are in close proximity to the tiles, every so often a random tile erupts, spewing an area with hazardous elemental energy. This trap has two triggers and two attacks.Perception     No Perception check is needed to notice the tiles, because they are readily apparent.     DC 25: The character notices a focus device located in an out-of-the-way place. The device likely controls the magic of the tiles.Arcana     DC 25: The character realizes that the tiles are channeling the energy of the Elemental Chaos, and each does so in a dangerously unstable way.     DC 30: The character recognizes the focus device as a chaos stone—the controlling focus for this type of trap— which can be overloaded with the right kind of attacks or through careful manipulation. Successful manipulation requires a character to use the same energy that the tiles spew during the round in which that character attempts to manipulate the focus device.Trigger 1A creature enters a square that contains an elemental tile. The trap then makes the following attack.Attack * VariesOpportunity Action      Melee 1
Target: The creature that triggered the trapAttack: +19 vs. FortitudeHit: 2d8 + 7 damage of a type determined by a d6 roll (1, acid; 2, cold; 3, fire; 4, force; 5, lightning; 6, thunder damage), and the target is slowed (save ends).Trigger 2Once enemy creatures are in the encounter area, roll initiative. On the trap’s initiative count, a random elemental tile explodes with primordial energy, making the following attack.Initiative: +2Attack * VariesStandard Action      Close burst 5
Target: Each creature in burstAttack: +19 vs. ReflexHit: 1d10 + 7 damage of a type determined by a d6 roll (1, acid; 2, cold; 3, fire; 4, force; 5, lightning; 6, thunder damage), and the target is slowed (save ends). The burst creates a zone of difficult terrain until the end of the trap’s next turn. The type of energy also determines the current vulnerabilities of the chaos stone (see Countermeasures).Countermeasures     Succeeding on a complexity 1 skill challenge (4 successes before 3 failures) using either Thievery or Arcana disables the trap. The characters disabling the elemental tiles must be adjacent to the chaos stone to make an attempt. Each attempt takes a standard action. On a failed check, all the tiles explode in the close burst attack.
     The chaos stone has AC 14, Reflex 14, Fortitude 28, and hp 100. When it is reduced to 0 hit points, the trap is destroyed. When the elemental tiles trap makes a close burst attack, its chaos stone focus is especially susceptible to the same kind of attack until the start of the trap’s next turn. During that time, a successful attack against the chaos stone that deals the same type of damage as the trap’s most recent attack automatically scores a critical hit on the chaos stone.

Published in Dungeon Master's Guide 2, page(s) 71.