Nogus was a Ta-Matoran when he was bitten by a shadow leech from a parallel dimension (accidentally brought by the dimension-hopping Vezon). This Shadow leech only drained elemental light. Later Nogus was made a Toa of Shadow.
The MOC looks pretty good, I like how you used the Metru torso, other than what others have said, the biggest problem that I have with this is that the Metru red needs to be distributed more throughout the front of the MOC.
The color scheme is way off. the secondary color is obviously Metru Red, yet there is none in the arms or upper torso, and it looks like it was thrown there only to fit the mask colors.
I think you can improve the arms and legs quite a bit, but this is promising.
I agree with @Saxton particularly about the head. However, that is often the case with the Kiril. It is easy to get a puffed up or stuffy look with this mask. One of my MOCs, Meku, has the mask, and the original version looked very stuffy (almost as though she was about to drown in her armor). With your MOC, there is also the added trouble of having a large amount of CCBS parts plating the fairly small body that’s underneath.
There are a few things that I think might be helpful to your MOC. First, bulking up the interior of your MOC to make it look more solid. Second, rearanging where the head is in proportion to the chest (that or finding a different method of admiring the mask, and possibly a different mask). Third, either choose a texture to commit to the whole MOC and stick to it (what I mean is that you currently have two textures that aren’t working together - the g1 on the arms and feet, and the CCBS pretty much everywhere else), or find a way to blend the textures.
All that said, the concept of this MOC looks pretty nice. I think with a little work here and there, this will be a fantastic Self MOC.