I feel like Diana should be added, once she hits 6 every lane pretty much soils themselves and needs summoners/escapes to live. She abuses mistakes heavily and snowballs easily.
I also feel like Shaco can be a really goofy but awesome pick in low elo. He doesn't need leashing so your laners can just stand in lane or scout for you, and his invasion pretty much dominates weak earlygame junglers and has so many ganking tools that he causes chaos in every lane he visits. He's pretty hard to execute correctly but i feel like a well played shaco will just eat a whole team alive and take objectives without response and win games single handedly.