I have try to calculate the species of mamono who have the largest population...so the specie you have the more chance to encounter if you are in this world...
1- The succubus: succubus have a reproduction rate very low but they become the more common specie because of merging women...The succubus can merge a women but almost anything in a demon realm also turn a women in a succubus (Air,water,earth...)more,some specie of mamono can merge a women in a succubus form...I guess the population of succubus will be 34% of all mamono...
2-The matango :We even don't know if a mamono can have a baby with her mate (I don't talk of husband,any men who breathe a spore finish his life to continually sex with her,even if she don't like him at start)but any women who breathe a spore merge into a matango after a while.So all refugees will end up send her spores in another city.After some time the entire nation finish as a matango nation.The matango are the only one who can turn a men into something other than a incubus so for me we can count the mushroom mens as matango too...I guess the population of matango will be 13% of all mamono...But they are concentrate in some place so you can travel without find one if you are careful...But if you see one of them,you surely have already breathe a spore...
3-zombie : for this one i'm not sure but i guess all cimeterry in a new demon realm will eventually create lots zombie.This is said they are created by the demon lord power but i assume demonic energy in a demon realm can be count as hew power.If i'm right,zombie will be 6% of all mamono (If,i'm wrong they are 0.04% of all mamono instead with undead mushroom who can merge a women into a zombie sometime...)