Failing to recognise the right-most character, at least for now, so putting up character_request tag. Also I'm just guessing multiple_monochrome can be used here, as one of the four parts of the picture isn't monochrome, but the other three are.
The rim of the hat visible at the top and the blood spatter would point to another instance of Koishi. But that would be strange. Maybe the artist just forgot he already drew her once...
A second guess would be Marisa, but she's missing her braid (which may be explained by the blood spatter there.
