Thoughts on Kallista
Since Kallista is causing such a stir, I have a few theories that might help explain this new champ. First off, Kallista has a lot of puppet mastery around him/her, I find this difficult to believe that he could be a "good" aligned champ, possibly chaotic neutral because of the black mist being more a form of nature then a malevolent force. Kallista is the spirits of the betrayed, come to seek their revenge (more on that later).
Also a lot of "sea" imagery and "flags" have been thoerised to be connected to him/her/it. So I think he/she/it is probably an undead pirate of somekind or something to do with ships and the sea, possibly inspiration drawn from the similarly named "Calypso" in Pirates of the Caribbean.
As we know, there are 7 champs that have black mist form around them on the website. All of these champs have betrayed and/or decieved people in their quest for power and most are evil. If this is an allusion to the 7 deadly sins then its possible all these champions will receive the "7 Deadly Skins" (See, the play on words there), each representing a different sin. Also Twisted Fate's cards are white on the website which is possibly an indication of him being "controlled" in some fashion by Kallista and the puppet "theme" is strong in the Harrowing Video too.