It just has a wrong texture.

That's been there for a while, basically we're waiting for the texture artist to make it for us.
Until then, remember, this mod is still a work in progress, so unless it's a game breaking bug that needs fixing now, Pahimar already knows.

No,you are wrong,bigbadchris makes textures for a lot of not-implemented stuff,just download the EE3 github file and check all the textures.

So there is.
Looking through the code for the Dark Matter bow, it would seem that pahimar just hasn't gotten around to adding the texture, or really any functional code, so I'm gonna just say that it's on the to-do list.

Ok,thanks,anyways the bow doesn't work at the moment.

Yeah, the only part of code for the bow is there to tell the game the bow exists. there is no functional code.