Alistar is a character I introduced in the fanfic My Fair Evil
, as a socially inept, uber shy shut-in who Jake helps get in touch with her social side. She's supposed to be a shapeshifter, but I tone her down into plainly a dark wizard or something.
Finn and Jake thought she was evil because of how she looked (and the crowd telling them that she's a witch who kidnapped a prince), but it later turns out that she's just lonely.
I'm planning to use her again in future fanfics. Her VO would be Shannon CHan Kent
Adventure Time (c) pen ward