Souls touched by Darkness wander beneath the Earth
soooo time to explain stuff. an event which I still have not named yet (name suggestions would be nice) covers a decent chunk of The Underground in liquid Darkness. The Underground was already bigger than the cannon Underground so now it's just slightly bigger. in the process a LOT of Monsters get misplaced and are either considered missing or dead. and while most are lost or dead some get a fate worse than death.
most Monsters Kris, Gold and Yōki encounter are just lost and scared and fight back with magic, but Darkened Souls often disguise as scared Monsters or manipulate the monsters vision of the world. the more Darkened the Soul is the more the mask slips however. when a monster touched by Darkness gets found out they tend to cry Liquid Darkness or black smoke like mist comes out of their eyes. dependent on the level of Darkness within a soul Gold can purify it using Determined Light, but when a soul is beyond saving it tends to corrupt the Monster's physical body mutate them horribly, exaggerating certain features and losing every ounce of what they used to be.
the Froggit is just lost and scared, the Whimsun is Touched by Darkness and has the smoke like mist, and the Shadowguy is beyond saving. Shadowguys are one of the more common enemies that can't be saved but it's not impossible to find one that can. I hope this post clarifies stuff for y'all