The developers made several April Fools jokes about a character known as "Urf The Manatee". Despite him never being a playable character, he has made an appearance in skins for the characters Warwick, Corki and Fizz. He was supposedly killed by Warwick, and on the Harrowing map, his ghost can come out and attack Warwick.

Ezreal's dance is based on the dance routine that appears during the ending sequence of the anime The Melancholy of Haruhi Suzumiya.

When playing as Skarner and remaining idle for a period of time while in a bush, there is a chance for him to say "Skar-skar-skarner!" This is a reference to the Pokemon game series, in which each Pokemon says its own name in a similar fashion, and can be found within tall grass.

When Braum feeds a Poro on the Howling Abyss map, the Poro will gain a moustache like his. The color of the moustache will change depending on Braum's skin.

According to Riot, Yasuo uses Pantene to keep his hair beautiful.

After waiting for a few seconds on the Victory Screen in the Howling Abyss, Lissandra will give a monologue about the events that transpired on the bridge.

In ARAM, if all players feed a single Poro with 10 Poro-Snax, the Poro will explode into multiple smaller Poros.

In Summoner's Rift, if Ahri wears the Popstar Ahri skin and dances in front of the Blue Sentinel, it will dance with her.

In the ascension game mode if all 10 players dance, Xerath will dance as well. If one player stops dancing so will Xerath.

By feeding a Poro with Braum, the Poro will grow a black mustache. When using the Dragonslayer Braum skin, it will grow an orange mustache instead.

If all Champions on a team wear the Pool Party skins (including Rumble in the Jungle and Surfer Singed), a rubber duck will spawn in the bottom side river of Summoner's Rift.

Before the release of Tahm Kench. Laughing in the river of Summoner's Rift would result in Tahm Kench laughing back. This only worked once per match and only before Tahm Kench was released.

The character Cho'Gath seems to be based off the character the Violator from the American comic book franchise "Spawn". This could be a coincidence, but when the game first launched, the Void (where Cho'Gath is from) was framed more like the world's equivalent to Hell, and the Violator is a minion of Hell.

The skin Dark Star Cho'Gath was made in collaboration with a critically ill League of Legends player named Bryan, who met Riot Games through a partnership with the non-profit charity the Make-A-Wish Foundation. Bryan wished to "meet the creators of Riot Games, and make a skin with them." Dark Star Cho'Gath was chosen between three skin designs and inspired by Bryan's love of outer space. The skin's theme music is based on a clarinet performance from Bryan. All profits collected from the skin until July 20, 2018 were donated to various non-profit organizations around the world.

The character Veigar seems to be based on the Black Mages from the Final Fantasy series. This connection is further backed by one of Veigar's skins, called White Mage Veigar, which has the white and red coloring of the White Mages from the Final Fantasy series.