An Abyssal runestone allows a spellcaster to cast lesser planar binding, planar binding, or greater planar binding, provided the spellcaster has prepared a spell of equal or greater level to expend during the casting; the planar binding spell functions at a caster level equal to the spellcaster's, not to the Abyssal runestone. Spontaneous spellcasters cannot use Abyssal runestones in this way.
If a chaotic evil outsider eats an Abyssal runestone, the runestone is destroyed and the outsider permanently gains the advanced creature template. A creature that already has this template, or is above CR 20 in power, gains no benefit from eating an Abyssal runestone.
Abyssal runestones may have several other uses as components in rituals and powerful magic, particularly in quickening the effects of afflictions associated with the Abyss—for example, the creation of a fast-acting, highly contagious variant of the polymorph plague (see Pathfinder #135: Runeplague) requires the expenditure of an Abyssal runestone.
An Abyssal runestone is destroyed if it is eaten by a chaotic evil outsider or used in one of the rare occult rituals that can be bolstered by its sacrifice.
- Pathfinder #134: It Came from Hollow Mountain
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