Mythals are enormous, layered magic constructions created by extensive and unique group rituals. They were designed to provide magical support to those in their area, but most have lost their power and now provide only protective fields to hinder enemies and help allies.
Effect: A mythal usually protects a large area such as a city or town. Most commonly have the following effects on creatures while they are in its area:
Evil or chaotic evil creatures take a -2 penalty to attack rolls, checks, and saving throws. In addition, those creatures cannot use teleportation powers.
Creatures allied to the mythal gain a +2 bonus to saving throws.
Any creature that activates a spellscar is affected by the mythal for the rest of that day as if it were evil.
Any attempt to teleport into the mythal’s area alerts any wizards that are linked to the mythal, and such attempts fail unless they have been specifically allowed. Those entering the mythal’s area arrive in a magically warded, well-guarded location.
Usage: Mythals provide protection from outside (and usually evil) threats. The protection of a mythal offers a good opportunity to defend a population center or stronghold from outside attack. If the characters are considered allies of the mythal, they can handle stronger threats while in the mythal’s area. Have the heroes defend the area against a powerful raiding party, or a horde of minions following a powerful leader. The encounter can be difficult or extremely difficult due to the mythal’s effects.
Published in Forgotten Realms Campaign Guide, page(s) 53.