Well, I've never written a critique, so here we go.

Lineart and anatomy: Very well done, as always. The tail is wondefully designed, and the neck, too. While I would have prefered longer frontal legs, and the thighs less fat... Left back shank have also such an innatural angle, too strongly marked, in my opinion. The back also draws a strange curve, but I think it is the character itself, isn't it?

Perspective: Nothing really to say about it, it is just a profile drawing, but I think some things must be fixed. The back right paw seems too close to the spectator, it is drawn on the same "line" of the left one. The two further fingers of the left frontal paw are too big, also. About the horns... I don't think they should be so far from themeselves, one of them should be invisible or almost, shouldn't it?

Colour and shading: The colours fix very very well the theme of the drawing, violet is usually a sad colour... The shading is also very good, not detailed, but it looks very very nice, I like this "glossy" shading.

Background: Of course it is a simple background, but the colour and the effect fix the theme perfectly. It makes me think at the viruses of a deadly ill. While, that white frame around the character doesn't look very good, white should be a "happy" colour that inspires serenity, I would have prefered it black.

Other: I liked very much the character, very original. It doesn't very often happen that people draw abstract things. Maybe Plague smiles to much, it seems an innocent smile instead of an evil one, I think that, for fix it, the brow should be "angrier".

Well, I hope I didn't bother you too much.