When a practitioner of magic casts a spell in Dark Sun, they do not draw on the Weave like they would do in the Forgotten Realms. Instead, they draw power from the life energy of everything around them, desiccating plants and bringing pain to ally and foe alike. This is called defiling.

Defiling

Defiling while casting a spell deals necrotic damage to every living thing except the caster in a radius around the caster's position. This damage is equal to four times the spell's level, and the radius equals 5 feet per spell level. For example, casting the 3rd-level spell fireball would deal 12 necrotic damage to each creature within 15 feet of the caster.

Defiling while casting a cantrip deals 2 necrotic damage to any target within 5 feet of the caster.

The necrotic damage dealt by defiling cannot be mitigated by resistance to necrotic damage. If a creature is immune to necrotic damage, they take half damage from defiling, as if they had resistance to it.

Defiling while casting a spell has a set of distinct benefits. If multiple effects from the following list would be applicable, only one effect occurs; the caster chooses which one of the effects their defiling causes.

• If the spell restores hit points or grants temporary hit points, the amount of hit points or temporary hit points granted is increased by twice the spell's level. If the hit points are granted to multiple creatures, this increase applies to all creatures affected by the spell.

• If the spell deals damage, the amount of damage dealt is increased by twice the spell's level. If the hit points are granted to multiple creatures, this increase applies to all creatures affected by the spell.

• If the spell subjects a creature to a saving throw, the save DC of the spell is increased by twice the spell's level.

• If the spell grants a beneficial effect to a creature without restoring hit points or granting temporary hit points, the spell can also affect one additional creature within 5 feet of the initially targeted creature, or within 5 feet of the caster if there is no additional creature within 5 feet of the initially targeted creature.

• If the spell requires an ability check, such as counterspell, the ability check made by the caster gains a bonus equal to twice the spell's level.

Preserving

By default, a spellcaster defiles when casting a spell. If a caster chooses not to defile while casting a spell, they can instead choose to draw the energy from their own body, which is called preserving. A character who chooses to preserve rather than defile might do so out of a desire to avoid contributing to the desolation of Athas, or might simply wish for stealthier, subtler spellcasting.

Instead of dealing necrotic damage in a radius around the caster like defiling would do, preserving while casting a spell instead deals necrotic damage to the caster equal to twice the spell's level. The necrotic damage taken by preserving cannot be mitigated by resistance to necrotic damage. If a spellcaster is immune to necrotic damage, they take half damage from defiling, as if they had resistance to it.

Using a magical effect that is not a spell, such as the Channel Divinity ability of clerics or the Hypnotic Gaze ability of enchantment wizards, activates defiling or preserving as if it were a 1st-level spell.