i have been experencing this since the mordekaiser rework. it happens only when there is him in a game and he gets on my screen i get something like 15 fps it's just straight out impossible to teamfight. Ive read a lot of other people are experiencing this as well on reddit. :(
Is there something you really can't do without in the client? Is Udyr displaying as a Picasso painting again? This is the place to report bugs and give suggestions for League of Legends in general!
Don't spam your suggestions or bug reports here, and follow the [Universal Rules](http://boards.euw.leagueoflegends.com/en/c/announcements-en/3eWpXbJi). While not every suggestion here will be implemented, your favourites can be voted to the top for maximum visibility!