Assassins is the way to go. Champs to khazix, and kassadin have a ridiculous dps and can really change the outcome of a teamfight. Just understand how to play an assassin. Get in, focus the adc, get out. Khazix has a nice leap which you can use to either engage, or you can use it to escape after getting the kill. Kass has an awesome ability which is basically a flash on a very low cd that can use to catch up, or escape. Those are the two assassins Id recommend to anyone looking to play those type of champs.