Word for someone who is jovial, but malicious?

I'm working on designing characters for a game, and the main group of villains consists of characters that have a two-word epithet in the form "The ___" where the word in the blank describes their personality or what they do (i.e. "The Languid," "The Reminder," etc.)

One of these characters acts like a trickster/jester, but in an uncanny and rather malicious way. (Think Batman's Joker or The Legend of Zelda's Happy Mask Salesman). Is there a word to describe this type of person? Basically I'm looking for a noun or adjective that includes meanings or connotations of "strange," "unpredictable," and "malicious."

Some near misses include "uncanny," "fickle," and "capricious." The latter of which comes closest, in my opinion, but doesn't quite encapsulate the connotation of malice or foreboding.

I might pick one of fay/fae as alternatives for fairy that focus on the older malicious trickster version and make it clear you don't mean a cute Tinkerbell type. One might find "The Fey Fae" both appropriate and either awful, amusing, or both.

The malefic (adj.):

1. Causing harm or destruction, especially by supernatural means

   'She was hypnotized by the spider's malefic eyes'

   Source: ODO

2. Doing mischief; causing harm or evil; nefarious; hurtful

   Source: Webster

The scapegrace (noun, archaic):

1. a mischievous or wayward person, especially a young person or child

   Origin: early 19th Century: from scape (see scapegoat) + grace, literally denoting a person who escapes the grace of God

   Source: ODO

I would use impish in this context.

http://www.merriam-webster.com/dictionary/impish

impish adjective imp·ish \ˈim-pish\ : having or showing a playful desire to cause trouble : playful and mischievous