I'm going to take a wild guess and say that it's likely the exclusive fig is that Overlord. That fig wouldn't be unprecedented.
No, we know for sure that it's not, because that Overlord would not be an exclusive fig. It's already coming in the Battle for Ninjago City set. The figs that come with the Visual Dictionaries and Character Encyclopedias are unique designs that never end up appearing in other sets.
The only near-exception is the Luke Skywalker in the revised LEGO Star Wars Visual Dictionary, who is based on (but still unique from) the original Luke Skywalker minifigure from 1999. However, there are several differences, most significant of which is that the new Luke minifigure has back printing while the classic Luke minifigure did not.
Chances are that the exclusive fig WILL be an existing character from the sets, but with a new design that does not appear in any sets. Compare how the exclusive Lloyd minifigure from the Character Encyclopedia appeared in his black costume from the Final Battle story arc, which did not appear in any other sets (the 2012 sets had his previous ZX costume while the 2013 sets only had him in his Golden Ninja costume).
Speaking of costumes that aren't really exclusive, it was recently discovered that the Zane minifigure from 70726 Destructoid
(the one with his robot parts concealed, which was previously thought to be exclusive to that set) will be appearing in a $9 activity book
, which will be a much cheaper way for people to get that minifigure. Destructoid is a good set, but I might spring for the activity book because its contents sound exciting and there are already lots of other LEGO sets on my wish list for this year.