1:Zilean,he is immortal,and controls time.He could literaly freeze time,go get a sword,cleanly slice off your head,and resume time.
2:Nasus,he is either a god,or very very close.He can and will rip your soul out.
3:Jax,he could 1vs200 with a weapon and win
4:Xin Zhao.He went 1vs300 and own.
5:Annie,when she reaches adulthood,she will be more powerfull than any other magician.
6:Fiddlesticks,not much is known about him,just that anybody who enters his sanctum dies,without exception
7:Soraka,ever been hit by a star?
8:Ryze,he wields ultimate power of Arcane power
9:Lux,just a very powerfull magician.
10:Nidalee,I am sure everybody will disagree with me,but come on,thinkg about this for a second
Those are the MOSTLY human ones
Anivia, Malphite, Renekton, Mordekaiser,Cho'Gath, Kog'Maw,Karthus,and Malzahar are super natural to the point of being gods.