personally
Wether its Graves or Jhin in the picture
I feel the victorious skin should have gone to a more deserving champion
Like
or
or even 
the more i look at this the more I think it's Gangplank. Looking at the left side of the image, we see something flat on the bottom. A guard from a sword? above the flat part is something jutting upward. The blade to a sword? What I'm imagining is a gun in one hand and a sword int he other.
Alternatively, the part on the left could be the rest of Jhin's gun, but at this point I'm leaning more toward Gangplank.
For a moment there I thought they were unmasking Jhin and I got excited as hell.
But it's probably Graves :/