source http://kurobine.sakura.ne.jp/
sorted according to the site number sort (date of creation??)

update: 2017/10/09 added 6 pic of 2 monster girls to the gallery top

Sea slime... also known as a Jellyfish, but sure.

Base +3, tobeunforgiven2 +16

The list just keeps growing.

Base +14, redmanticore +6, tobeunforgiven2 +16

Wait... Female Ninjas are considered monsters now?

Base +6, tobeunforgiven2 +16, wenx° +2, racer0522 +3, FlowerSlaughter +7

This is proof Japan cracked the secret to awesome women. Apparently all one needs to do is increase the bust size, change the ears, and add a tail, and you have waifu gold. And we're all happier for it.

Base +3, blackforest25 +1, eldbetha +1

@Meachi
Lore reason: When the new Maou took over some human ninja ladies got turned into succubi. As they're succubi now, the encylopedist saw fit to include them.
Flavor reason: As females who kill men utilizing sexuality, and with an entire continent based on Japan already established and in need of fleshing out, adding kunoichi to the setting as monsters couldn't make more sense.
Real reason: Sexy ninja lady make penis hard

Base +7, repeatedmeme +9, FlowerSlaughter +7