Cassiopeia passive idea
There was another thread suggesting something similar to rengar's trophies, but I can't seem to find it.
Basically, why not give her a trophy each time she stuns an enemy champion with her ult? I guess she isn't quite Medusa but I think she's close enough for the idea of her creating a "stone garden" or whatever with each enemy champion she stuns with her ulti.
Whether or not this would be the only stacking mechanic of her passive (including or removing the current one) could be decided separately, as well as the rewards. This is basically just a thematic idea I had in mind that I thought would work well with her identity.