Complex sentence: His proficiency is due to taking ten levels in the obscure prestige class Dashing Swordsman, allowing him to apply his high Charisma bonus to attacks with a rapier, provided that he makes a witty remark while doing so.
Split into simpler sentences: His proficiency is due to ten levels in the obscure prestige class Dashing Swordsman. This class allows him to apply his high Charisma bonus to attacks with a rapier, provided that he makes a witty remark while doing so.