Nature-themed realm with a Deer-like champion
The world could be like Riot's interpretation of the Emerald Dream dimension found within WoW.
The Deer champion could be like the great guardian of this all forested dimension, making sure that the tranquility of the forest is always at a balance.
http://www.comicartfans.com/Images/Category_42685/subcat_87741/Cenarius.jpg
http://img12.deviantart.net/6ac7/i/2014/224/c/0/xerneas_fan_art_by_houndourka-d6n7qaf.jpg
The first one is Cenarius, from Warcraft, while the second is Xerneas from Pokemon. Riot could start off by drawing inspirations from these 2 fictional characters, since both of them are inspirations from Cernunnos the Horned God, a Celtic deity.
It could even be a cool way of legitimately introducing Unicorn-like champion
Also, depending on what direction they would take this supposed Deer champion, they could introduce a Druid-based champion as well. They could be like the 'Malzahar' of this world, in that she/he would be a human from outside their realm becoming empowered with Druid powers. The champion would be able to summon different kind of nature beasts or like the spirits of beasts that would work in a similar way that Syndra's spheres work, in that when piled up together its more effect, because her/his ultimate would make all beasts currently out charge towards the target like a stampede of many different animals. Also, these summoned druid beasts would attack its surrounding enemies wherever it's placed, but will not be able to move since that would probably too OP
https://s-media-cache-ak0.pinimg.com/236x/64/47/48/6447489b51343372607bf5a7e831ce3f.jpg
