A great many spells have esoteric effects, possibly limited to just within the target's mind or soul. Rather than butt up against the target's Protection score or their Elemental Resistances, these may go against their Magic Resistance instead.

What even is Magic Resistance? That is purposefully left vague. It could be the unit's mental willpower (like a Will save in Dungeons & Dragons). It could be their creativity or intelligence. It could be their attunement with magic, or perhaps even their discord with it. It could even be their soul. Maybe it's just that field beings have in Neon Genesis: Evangelion.

Regardless of what Magic Resistance is, it serves as a base for a DRN roll against the offending spellcaster's Magic Penetration.

The offender's Penetration varies mainly on what is being cast:

• Most effects have a base Penetration of 11. If the effect is known to be "easy to resist" or "easy to negate", its base Penetration is 7. If the effect is known to be "hard to resist" or "hard to negate", its base Penetration is 15.
• The caster then receives a Penetration bonus equal to half of their "overcast"; this is the gap between their skill level in the spell's primary magic path and the bare minimum skill level required. For example, a 4 Astrologer casting Mind Burn without any assisting items has a Penetration of 12. This doesn't apply to all spells, and it rounds down.

The caster also gets a DRN roll added to their Penetration, but this competes with the defender's DRN roll.

Against a spell effect of a magic path they know, the target gets a Magic Resistance bonus equal to half their skill level in the effect's assigned magic path. This is presumably because they understand what they're being hit with on some level. For example, the paralyzing effect of Astral Shield is an Astral spell effect; possessing two or more Astral levels makes an Astral Shield less likely to paralyze you, if you intend to punch through the shield instead of using your own magic. In some cases, this bonus is offered even when the Penetrator isn't offered theirs.

The Penetrator wins ties. The only time the Penetrator doesn't win ties is when their Penetration bonuses don't apply.

Against most effects, Magic Resistance either works or doesn't work. Against some magic, however, Magic Resistance only halves effects. Examples include the enervating light of Stellar Cascades and the enervating darkness of Shadow Bolt.

In addition, some magic has secondary or tertiary effects that may require additional Magic Resistance rolls to prevent. In certain cases, you can resist the main part of a spell, but still get hit with the side effects. For example, the odds of resisting the damage of a Nether Bolt but still getting Feebleminded are low, but never zero. A fair amount of spells have side effects that really only matter if the main part of the spell is resisted, such as Syllable of Death attempting to Fatigue the target after either succeeding or failing to "instakill" them.