This is the split 2 emote for playing ranked, similar to the Victorious Morgana icon from split 1. I'm fairly certain this is our first look at the new Mordekaiser who should be released sometime during split 2, unless I'm overlooking a skin somewhere. I thought it could be Death Sworn Zed for a second but there's not enough blue fire.
The shape of the helmet is roughly similar to Morde's iconic design, with blue eyes to match his Shadow Isles subjects. I gotta say this gets me pretty excited. I did like that he originally had a completely different color scheme to the other Isles champs because his undeath wasn't started there, but his necromantic power does synergize with the Ruination's so it does make sense. We also don't know how much the lore is getting changed so something else could be the cause.
Or maybe I'm just rambling about something I don't know and this is a long lost skin I haven't seen in years, who knows.