Wights
Wights are a walking collection of swelling tumors and polyps on the verge of a massive, violent explosion.  These wights amble toward their target and then drive a dagger into themselves which results in a huge explosion spewing paralyzing pus everywhere. 

Strengths:  Well, they smell bad.  Is that a strength?  They can sneak up on you, especially if the map isn't turned on.  They have a proximity fuse and will blow themselves up if you get close and then turn away.  In multiplayer they are great for taking out thrall since you can submerge them and most people hide their thrall in the water.  They are immune to confusion and paralysis.  

Weaknesses:  Wights are very weak.  Three arrows or two sword slashes is all it takes to pop one.  J-men are resistant to their explosions and immune to their pus.  A good way to pop a wight is for a J-man or Heron to get fairly close (but not too close!) to the wight and then run away.  This will trigger the wight's proximity fuse and he'll pop himself.  It's a bad idea for any unit besides Jmen or Heron to try this because they don't have the same advantages over the wights.  Also, a heal from a J-man or Heron will un-kill them. 

Vitality:  5.5
Damage per hit:  5-6 (explosion) 
Range:  0-2
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