Frost Fang Cassiopeia
I wish I was an artist to conceptualize some visuals for this idea, but sadly I am not. However, Cassio is a cool champ and I own all of her skins except Siren and I think she has so many great possibilities for skin particles/effects, but none of her skins really offer much other than a color change, if that, so I kind of came up with an icy concept for her! :)
Q - a puff/burst of blue with some shiny ice crystals (sort of like the Corki phosphorous bomb particles)
W - an icy field....maybe even a swirl of icy mist around it or even icicles falling from the sky...
E - obviously it would just be an ice spike, unless some other clever idea is mustered up :)
R - Her ult could be something as cool as ice spikes shooting out and stick through the enemy champion to root them, or just keep it simple and changing them into a blue color until the stun is over. if they only get effecting by slow then maybe some blue feet, or just a nice icy trail!
These are just my basic ideas. If you have any skill effect suggestions I'll add them in too, but I think its a really fun skin for her and fits her stone/slowing concept. And she needs something different and fun and not just color changes! :)