Djezet

Djezet is a rust red metal that's liquid at room temperature and extremely reactive to magic. Critical hits made with djezet ammunition against a prepared or spontaneous spellcaster cause the target to lose one prepared spell or one spontaneous spell slot unless the target succeeds at a Will save (DC 30 for standard grade or DC 40 for high grade). The slot is randomly selected from among the caster's highest three spell ranks (and then from among the spells prepared in that rank, for a prepared spellcaster).