Illumians are the physical embodiment of a magical language, so they interact strangely with symbol-based spells. This group includes all spells whose names contain the word glyph, rune, sigil, or symbol (such spells in the Player's Handbook include explosive runes, glyph of warding, greater glyph of warding, sepia snake sigil, and the various symbol spells). When an illumian encounters such magic, one of two things happens: Either the illumian's resonance overpowers the spell, or the foreign magic corrupts the mystical language that defines the illumian. Illumians have a —4 racial penalty on saving throws against these effects if their level is less than the caster level of the spell. If an illumian's level equals or exceeds the spell's caster level, she is immune to the effect.