[s1e7] — Something Blue

goes blind because Willow mentions he "can't see anything." Xander becomes a literal "demon magnet."

While grieving her breakup with Oz, Willow attempts a "Truth Spell" to ease her pain, but her grief-stricken intentions cause the spell to backfire. Instead of finding clarity, her every spoken word becomes a literal reality. This leads to the famous comedic subplot where Buffy and Spike suddenly believe they are madly in love and decide to get married. [S1E7] Something Blue

Willow's "draft" was meant to be a simple spell to help her "will be done," but because her essence was so magically raw, it became a powerful, uncontrolled command over reality. The Resulting Chaos: goes blind because Willow mentions he "can't see anything