this is pretty unclear
who or what is the character in black?
She's the character from a previous chapter, March! :D
You can spot her here: http://beyondtheordinary.thecomicseries.com/comics/164
(She's a Mare, according to the folk lore she sits on peoples chests, while trying to strangle them when giving said people nightmares.)
I hope that cleared it up a little! :D