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The King of the Dead (along with his goons)
Strengths: Can't be killed except with the sword of Elendil; able to activate skull avalanches
Weaknesses: Can be killed by Isildur's heir (if he wields the sword of Elendil)
Disorder (mental): Bipolar*; obsessed with being cursed
Favourite Food: Doughnut holes
Probable Cure: Being released from the curse by Aragorn
Warning: Skulls are dangerous. Do not touch.
Orcs (in general)
Strengths: Bravery; loyalty; persistence; initiative
Weaknesses: Almost everyone kills them on sight, which could make survival for them difficult
Disorder (mental): Do whatever they are told (that is, by evil people)
Favourite Food: Pizza**
Probable Cure: Saruman should research and see whether it is possible for Orcs to reform.
Warning: Reformed Orcs may still get killed by everyone who sees them because of their general reputation. This suggestion is not guaranteed to work.
The Nazgul (aka black riders)
Strengths: Look really scary and awesome; ride dragon-like creatures; terrify all with their screams; can see you when you wear the Ring
Weaknesses: Cannot see very well, and so must rely on hearing and smell most of the time
Disorder (mental): Obsessed with Rings
Favourite Food: Oreos
Probable Cure: Sauron being defeated
Note: It is hoped that when Lord Sauron is defeated (if ever), his servants will be released from the Ring spell. However, we are not sure that it will actually work.
*The King of the dead and his goons are evidently bipolar, because when Aragorn said he would release them from the curse they initially refused. However, after accidentally activating a skull-slide, they quickly accepted the soon-to-be-King's proposal.
**Seriously. Orcs love pizza. Ask any Orc what his favourite food is, and he'll tell you pizza.