I usually write him as normal human, but the scope is there. I have
♦ turned him into a demi-god (thanks to a combination of the Kingman's Bluff incident, the Empowerment spell (since he was in the vicinity) and Willow fixing his eye (because, please!)), and
♦ made him into Willow's kind-of-half-kind-of-full brother (identical twins and Jack O'Neill were involved: enough said) with contact magic powers (ie, he affects things through touch) (oh, and he and Willow were Buffy's half-siblings through Jack)
The possibilities are endless, especially when you add in Halloween. Fun times!