Update: Yes, it’s “Lil’ Devil Teemo.”
After a confusing week of nobody being quite sure of who was in the Harrowing teaser image Riot released last week, the company released an updated version of the teaser today. This time, instead of a smokey spirit emerging from the cauldron, it looks like it’s a (more) demonic version of who we think is Teemo!
The middle figure is most likely Teemo given his history with being called a demon and the like. There is a possibility that it could be Veigar, given the little power orb and staff, but we haven’t seen Veigar’s face in the past and the character’s expression with his eyes closed screams “Teemo.”
The girl on the left is almost certainly Tristana, since it can’t be Poppy or Lulu (because they’re getting Star Guardian skins) and it can’t be Annie (because she already has a Harrowing skin.)
The one on the right seems to pretty clearly be Morgana, unless Riot is throwing us for a loop and it’s an extra-spooky Kayle.
The Harrowing is a special Halloween event that Riot throws together every year. There are special game-modes sometimes involved, like Hexakill: Twisted Treeline, but mainly a release of special spooky skins.
The skins normally go back into the vault after the Harrowing ends, so you have to grab them while you can or else wait until next year.
These new skins should be showing up on the Public Beta Environment very soon, since the previous PBE cycle is wrapping up.