Can't fight what you can't see... you can't see ninjas... the ninjas can't catch you if you're on fire... you can fight what you can't see if you're on fire. LET'S DO THIS!!!
Also, Weresheep + Yeti the ultimate in warm sleepy cuddles.
Wurm + Ushi Oni
High Orc + Hobgoblin
Leads a unified group of the two Mamono, strong and intelligent at fighting and sex, still kinda slow in other areas, giant breasts are a weak point. Once she falls in battle, she affects both Orcs and Goblins like the High Orc does.
Tempting... Very tempting...
I'm surprised you didn't go for the Dark Hellf, Jova.
Valkerie + Cupid
Shirohebi + Will-o-the-Wisp
The embodiment of a clingy girlfriend. She'll follow you throughout this life AND the next one. I imagine her tail having the bluish-white flame of a Will-o-the-Wisp and she can control whether or not it burns. If she gets jealous, she can wrap you up in her tail and let the fire burn you. By burn, I mean it has the same properties as the shirohebi's, so it will make you lust after her and her alone.
Dark elf isnt really that interesting to me. Yes I do like quite dominant girls, but I'm not anyones "slave"
A Apophis + Bicorn would be interesting or dark Valkyrie and a nurarihyon = once she finds a Master she would exude an aura that would attract only mamono that suit her Masters preference, it would be particularly effective towards angels and their variants like Cupid's and Houri.
A dark mage + witch
Result: Some kind of mega sorceress I think.