User blog comment:HozzieHozzbourne/Strongest champion outside of the game/@comment-7843294-20130921020531

Ahri, given enough time, could probably reach power levels similar to the previously mentioned champions. While it didn't outright say it, her lore implies that Ahri could attain nigh limitless power if she kept absorbing life. Once she did reach that level, she would be hard to stop considering her magu=ic would be fueled by the life of her fallen victims.

Yorick is also fairly powerfull, being one of the few beings in Valoran able to completly kill an undead. There's also that fact that he is literaly not allowed to die until he has "Buried his quota"

Elise as well, could in theory reach infinite power. As long as she keeps sacrificing her followers to Vilemaw.