Nasus us super buggy

Hi! Just wanted to explain a glitch. Whenever I play a game with a Nasus, my FPS drops below normal for no reason. It doesn't make any sense. I usually run the game at 200-250 fps on max setting but whenever he's in the game it drops to 80 and has spikes down into the 30's. Please fix. I know it's Nasus because I've played with it many times and it only happens whenever he's in the game.