The amount of people and spirits it has killed is off the charts. The Wraith.
The Wraith is an evil spirit first mentioned by Dezadon in Chapter 7. The Wraith kills anything it touches, and can make clones of itself.
The Wraith is the primary antagonist of another game made by SuperCloud9, known as The Wraith. Players are teleported into a randomly generated maze where they must escape The Wraith. This is alluded to by Baller and Crusher's conversation after Arcane and Dezadon talk about the evil spirits.
The Wraith has the power to drain one's mana through direct contact. The Wraith also possesses extreme regeneration capabilities, and is not known to be able to be killed by anything other than possibly the Asudem, though generally the two avoid fighting each other. However, the Wraith is vulnerable to attacks that use Arzen, though they will only temporarily incapacitate it.
-The Wraith will not be a boss fight in BFS. His only existence in the game is to link the universe of The Wraith and BFS together.