My theory towards the teasers.
Everyone who is a League player knows about the teasers that have come out, and now that Vi's teaser is out, I'd like to present my idea as to what this new champion could possibly do: He/she/it uses the elements as a source of damage.
What do I mean by elements? Well, think of Avatar: The Last Airbender elements; Air, Water, Earth, and Fire.
Seem strange or confusing? Allow me to explain.
The two most obvious teasers that point to this are Sona's and Vi's
http://3.bp.blogspot.com/-HVMJ6VUUGKQ/VoG1d7t-6nI/AAAAAAAA2W8/N2IWF2Xbw8E/s640/sn.jpg
Sona's teaser represents Air, using mostly the color white, and the animated portrait displaying what looks like butterflies or doves flying past her. Now, air is somewhat difficult for an artist to portray, due to it being pretty much invisible. Thus, it is usually portrayed by either clouds or smoke. And what happens to be coming out of Sona's mouth?
http://a.disquscdn.com/uploads/mediaembed/images/3005/5303/original.jpg
Vi's teaser represents fire. Using very brilliant reds, and the animated portrait displaying a firey glow with smoke and embers. Also, it somewhat appears as if her gauntlets actually melted off of her arms due to the extreme heat suddenly coming off of her.
The two less obvious ones are Garen's and Zed's. I'll start with Garen.
http://2.bp.blogspot.com/-SlHvPVSacbY/VoRacyeqTYI/AAAAAAAA2Xk/1_jj29gWPe8/s640/garen.jpg
Garen's teaser represents water, but in an unusual way. It isn't as if Garen is being drenched in rain, or being hosed down. Instead, it appears as if he is shattering or breaking into several pieces. However, water doesn't have to be represented in its liquid form. If too much weight or force is put onto ice, it will shatter. Also, some glaciers tend to be blue/green in color, which is the same kind of coloring Riot uses here.
Zed's teaser represents Earth, but no one would ever think of it at a first glance. In fact, you really have to look at the other teasers before you can safely assume that rose petals and branches represents Earth. However, Earth doesn't have to be represented by just rocks and dirt, or mountains. Instead, Earth can also be represented by plant life, such as trees, grass, roses and branches. But why use roses and branches, and not some sort rock for Zed's teaser? Well, I think we can find the answer from Avatar itself.
In the show, the element Earth is said to be the "strongest" element, in such that it cannot be moved, and the bending style follows this. Earth benders used a slow and forceful approach to their bending, with every time they sent a rock flying through the air, you knew it would hurt. Now, if we look at all of the teasers, they all tend to have a sense of elegance to them. They are meant to be beautiful in their own way, and invoke thought. I don't know about you, but for me, a rock isn't very thought provoking, or elegant. Thus, Riot moved to the less obvious representation of Earth, and used its more elegant and beautiful side in order to have Zed's teaser fit with the rest.
And thus, due to all of this, I believe we will be seeing a champion who is able to control the elements in some way, in order to do his biding, just like the Avatar. However, it'll all come from some sort of gun. All the teaser videos start off with what sounds like a gunshot, and the teasers all follow the "Deadeye" name. Will it be a new marksman? I don't know. We'll just have to wait and see.
