Okay, for my first proposal for a new Monster Girl,I have the graveknight. Graveknights are soldiers and warriors who were seduced and ravaged by a succubus, but attempted to escape their fate by taking their own life. Unfortunately, the succubus' power extends to beyond death as well, and these great warriors rise again as the strike force leaders of the demon realms, graveknights. When a graveknight is born, she becomes bonded to her armor in a manner similar to a lich and her phylactery. The armor contains the graveknight's essence, and an individual who is 'killed' can reconstitute herself so long as any part of the armor remains intact.
However, the armor also serves a second purpose. Because of the graveknight's mixture of differing demonic energies absorbed from the battlefield, her own demonic energy is warped and enlarged, creating a much more potent lure for human males. This lure is so powerful, that allowing it to simply air out like a normal monster would cause males to actively seek them out, and ultimately interfere with the graveknight's duties. The armor acts as a shell to prevent this, and contains the scent of the demonic energy.
Occasionally, though, a graveknight will encounter a human who is a particularly skilled fighter. In this occurrence, she will challenge the man to a duel, and if he sufficiently impresses her, she will open the face plate on her helmet to allow him to sense the demonic energy, and become her loyal follower. Men who are entranced in this way do everything in their power to satisfy their graveknight mistress, including fulfill her sexual desires to the utmost.
Conversely, if a human who is challenged is able to defeat the graveknight, she will immediately praise his strength and skill, and pledge herself to him. A graveknight who has made this pledge will protect the man from any and all threats, and will treat him as a lord while in public areas. In private, though, her demeanor completely changes, as her monster lust shines through for the man who proved himself her better. She will rarely wear her full armor, and her demon energy changes drastically. Because she no longer sees herself as "the one in charge", her energy will no longer dominate the thoughts of other men, and lure them to her. Instead, her energy focuses solely on the man she has pledged herself to, acting as an intoxicating aura that makes his own lust grow to extreme levels. A man who gives in to his lust will find himself being pleasured by the graveknight with as much skill as when she fights. She will use her whole body to find her man's greatest desires, and exploit them with as much expertise as when exploiting an opponent's weak points in their armor.
Alright. I think I covered all the most important parts. Anyone who has something to add, please comment and let me know.