After the evenings spell casting, Amy’s character takes a darker twist, as it emerges that she knows a warlock (called Rack) who can cast spells that “last for days with a near zero burn out factor” (i.e. they won’t get tired from casting too many spells).
As Rack deals in black/dangerous magic, Amy starts to wander and becomes hooked on power and jealousy (e.g. Buffy finds her attempting to steal magical supplies from her friend Willow because “she needs them”). This eventually leads to Amy placing a “Hex” on Willow, because she can’t handle the fact that she has to “work twice as hard” to be “half as good” (with regard to spell casting).