Here're a few more :)
Name: Swordsong
Strength: good
Dexterity: great
Speed: fair
Attack type: see below
Special abilities: the Swordsong has a melee attack which can be used from a distance, i.e. it is a ranged attack which ignores anything in its path, and doesn't lose accuracy for travel.
Behaviour: keeps its distance, and retreats when char closes in on it.
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Name: Swordance
Strength: great
Dexterity: great
Speed: great
Attack type: melee
Special abilities: the Swordance is in an everlasting state of a Whirlwind attack. It also cannot spend a turn in the same spot, and therefore will never move into an occupied spot, though it causes double damage if cornered into such a situation (surprise! ;) )
Behaviour: mostly normal, though the special abilities make this innately different.
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Name: Mindrape
Strength: poor
Dexterity: poor
Speed: good
Attack type: ranged
Special abilities: I have three versions of this monster thought up here:
1 - spawns with several monster illusions, based on whatever's around. They all then act normaly, while the Mindrape is disguised as one of them, and it can swap places (and form) with any of these at any time. It will often switch when hit, but will never switch into something that was just hit itself.
2 - ability has a long casting duration, and when ended, sends char into a small arena-like room which is effectively the chars own mind. There, he must battle something: a horde of demons, a small group of out-of-depth demons, the Mindrape's psychic form (which is much more powerful than its body), or even himself. Once done, he returns to the battlefield. Problem is - while locked in his own mind, the body is left vulnerable to attacks, so this one'd be damn hard to survive unless he's a lone boss (plus, as a boss there'll be alot of room for a very unique Willpower-based "special level").
3 - probably the simplest to implement, this version makes all other monsters invisible once he's in the char's LOS, and this can only be ended by killing the Mindrape - retreat is futile. Also, berserking is impossible within the Mindrape's grasp. LOS turns blue while under the effect, to signify the mindset of a violated psyche. The Mindrape might be a stealthy blue, or a burning, taunting red, depending on the Mindrape's "personality".
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Name: Mantrap
Strength: great
Agility: fair
Speed: N/A
Attack type: melee
Special abilities: the Mantrap looks like a tree, sounds like a tree, and bites like Shai-Hulud.
This one can really get the player paranoid ;)
Every turn the player spends near a Mantrap, there's a chance of it attacking, and the more time it waits, the better the attack is aimed (part Mantrap preparation, part unsuspecting char - so the bonus to-hit may grow also when the char's no longer within range).
Behaviour: it often waits 4-5 turns before attacking, but if the player moves around alot, that could mean going past the same Mantrap several times before finally being bitten with lethal accuracy.