The Lore Category
In 2010, Riot announced a new champion, Urf the Manatee, but before he could be released he was eaten by THIS champion first.
Warwick
Viego's lore revolves around his dead wife, whose tragic passing drove him to turn the Blessed Isles into the Shadow Isles, in an event known as The Ruination.
Isolde
Not dead, but in a Lunari Temple hidden in the Spirit Realm, Aphelios' twin sister is able to provide him with his 5 spirit weapons.
Alune
After cleaning up bugs where Syndra and Poppy could carry Baron Nashor or Dragon all the way to the fountain, what one champion can still displace Epic Monsters.
Bard (R - Tempered Fate)
Anivia and Gnar can use their passives to change their in-game chat names to Eggnivia and Mega Gnar respectively, but which champion can change the in-game chat name of your opponent?
Lulu (W - Polymorph -> Harmless Critter)
A basic attack that is not interruptible is classified as having an uncancellable windup. Commonly known as Bluetooth autos, basic attacks with uncancellable windups are only stopped by death, polymorph, untargetability, and 1 specific champion's E ability.
Quinn (E - Vault)