Confounded Rules! Spotlight: Magic Resistance

Some monsters' ability to resist the effects of magic, or magic resistance, is another woefully under-explained concept in First Edition Advanced Dungeons & Dragons. This article explains how this ability functions in the game.

In Advanced Dungeons & Dragons (AD&D), both First and Second Editions, some monsters possess Magic Resistance. This power prevents magic from affecting a monster with Magic Resistance as long as the monster passes a Magic Resistance check. Magic resistance helps maintain game balance. First Edition recognizes that spells and magical powers can easily dominate a game. Left unchecked, they would reduce non-spellcasters to near irrelevance, especially compared to high-level spellcasters. Magic resistance, along with the maximum number of spells known, the need to roll to “Know Spell,” spell disruption, casting times, and spell memorization, helps maintain this balance.

Expressed in 5% increments, this special ability—an innate magical power—causes magic to fail to affect the creature. This power is passive; it is automatically and continuously active. The monster needn’t concentrate to use it. In First Edition (but not Second), Magic Resistance scales with the level of the caster who casts the spell directed at the monster. The listed Magic Resistance is set for magic from an 11th-level caster. Therefore, adjust the listed value by 5% per level above or below the 11th. Magic resistance does not extend to other beings, even if a magic-resistant creature is touching them. A creature’s Magic Resistance does extend to all worn or held possessions, such as weapons and armor.[1]

For example, a spell is cast on a monster that has 50% Magic Resistance.

1. If the caster is a lower level, increase Magic Resistance by 5% per level of difference from 11th. Example: The monster has the equivalent of 70% Magic Resistance against a 7th-level caster (11 − 7 = 4, or +20%).

2. For higher-level casters above 11th level, the process is reversed. A monster’s equivalent Magic Resistance against a 15th-level caster is 30% (11 − 15 = −4 or −20%).

3. Any Magic Resistance of 100% or higher automatically blocks the spell without the need to check the dice. The converse is also true: Magic Resistance adjusted to 0% has no power to stop a spell.

This makes lower-level casters weaker against magic-resistant monsters and higher-level ones more powerful.

The table below lists all possible Magic Resistance combinations for easy reference.

The Changing Explanation

The explanation of how Magic Resistance works changed substantially between the First Edition rulebooks. The wording in the Monster Manual says a spell will “absolutely fail” when cast in the presence of a creature with Magic Resistance. This suggests that Magic Resistance, in effect, has an undefined radius around it within which it cancels a magical effect, much like dispel magic does.

Later descriptions clarify how Magic Resistance works and define it with a much narrower scope. Deities & Demigods (Legends & Lore) defines it as the “chance of any spell absolutely failing to affect the magic-resistant creature.” Similarly, Monster Manual II defines it as the “chance a spell might fail when cast on the monster.” This distinction, along with the fireball example in the same text, is important because it makes clear that Magic Resistance does not act as a dispel magic but as an immunity possessed by the creature.

Magic resistance can, however, cancel an existing spell effect in some cases. It notes that “The percent of magic resistance of a creature has an effect on certain existing spells, such as hold portal, where it indicates the probability of shattering the existing spell.” The keyword here is “certain,” which suggests a narrow scope for which spells are shattered (i.e., dispelled or canceled) by contact with a creature with Magic Resistance, rather than the broader interpretation that it functions as a pseudo-dispel magic.[1]

Magic resistance is always checked in the following instances. Note that even if the Magic Resistance roll fails, the monster receives a saving throw (if any) against the spell’s effects.

1. When a spell is cast that would affect a monster with Magic Resistance, the Magic Resistance check determines whether the spell takes effect. For example, if a suggestion spell is cast on a monster, a successful Magic Resistance roll means the spell has no effect. For area-of-effect spells, such as fireball, a successful Magic Resistance roll means the spell has no effect on the monster, though it would still affect creatures without Magic Resistance within the area of effect.[2]

2. When a monster with Magic Resistance encounters the effects of a spell already in place, it can resist those effects. For example, a monster that succeeds on a Magic Resistance check can walk through a stinking cloud without being harmed. This also applies to spells meant to keep out monsters. Likewise, a demon with Magic Resistance whose check succeeds could pass through a paladin’s innate protection from evil ability and attack the paladin.

In some cases, such as with ”certain existing spells, such as hold portal,” a successful Magic Resistance check cancels the spell.[3] What exactly constitutes an “existing” spell is left for the DM to interpret. Whatever the exact spells are, they should have a narrow definition. Wizard lock almost certainly falls into this category, given its similarity to hold portal. Other barrier-creating spells may as well, though the rules do not specify.

Magic resistance does not apply in these instances:

1. When a monster with Magic Resistance casts a spell.

2. Magic resistance cannot prevent magic items from functioning as magic when employed. Additionally, Magic Resistance cannot prevent a magical weapon from striking a creature with Magic Resistance or nullify the weapon's magical properties; therefore, no Magic Resistance check is required.

3. When a spell creates a permanent effect, such as a wall of stone, Magic Resistance is not checked when the spell creates the permanent effect. Similarly, Magic Resistance does not apply to indirect effects from magical sources, such as the light from a continual light spell.

4. It has no effect on anti-magic effects, such as an anti-magic shell or a beholder’s anti-magic ray.

One issue with Magic Resistance arises when a creature with Magic Resistance is the recipient of a beneficial spell, such as a cure light wounds cast by another spellcaster. The rules do not explicitly state whether the recipient may voluntarily lower Magic Resistance to receive the spell’s effects, or whether they must first check their Magic Resistance to determine whether the spell’s effects apply. Second Edition states this explicitly, though First Edition does not.

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