The Foxfire skin for Ahri, Safari skin for Caitlyn, the Explorer skin for Ezreal and the Chrome skin for Rammus all reference Internet Browsers Firefox, Safari, Internet Explorer and Chrome respectively.
Less than 0.5% of all players on League of Legends actively play the Dominion gamemode. This in turn led to the eventual removal of this gamemode entirely, until it's return in the game's rotating gamemode queue.
Each and every Champion has a set of four in-game emotes, activated by the keyboard command Ctrl+(Number key 1-4), consisting of a joke, taunt, dance and laugh. Many Champion's dances are references to various pop culture and internet memes. Twisted Fate's dance is the obligatory Gangnam Style by Psy, Corki is a reference to the "Do a Barrel Roll" meme, one of Amumu's skins, Emumu, changes this champion's dance into a reference to a goth South Park character, and Volibear's dance is a reference to an America's Got Talent contestant.
When the Champion named Jhin was teased in late December and early January, he was teased via short clips of art depicting four Champions, Zed, Sona, Garen and Vi, appearing to be shot and possibly killed by Jhin, with numerous effects encompassing them(Oriental flowers and vines for Zed, wisps of smoke and ethereal butterflies for Sona, shards of crystals for Garen and smoke and flames for Vi) when first accessing their respective web pages on the League site. The four Champions, and Jhin, make up the standard team composition in League of Legends, the top-laner(Garen), the mid-laner(Zed), the jungler(Vi), and support(Sona) and the attack damage carry(Jhin).
During the development of Jhin, another champion that was released before he was, Kindred, stemmed off an initial concept for him. Kindred's bounty hunter-style passive was originally going to belong to Jhin, following the bounty hunter sniper theme that was originally planned for him. Once the concept was scrapped however, this passive ability went to the personification of Death that was, Kindred.
The Star Guardian Lux skin is a reference to the popular anime series "Sailor Moon", which goes as far as referencing the series' iconic Sailor Moon stance used by the protagonist, which Lux imitates as a part of her recall animation.
The Champion Karthus resembles a form of skeletal necromancer, with whatever skin showing in the form of empty bones. In China, the splash art for the character depict Karthus with a shadowy face and menacingly bright eyes. This is because bones and skeletons are considered taboo in China.
The two Champions, Vi and Caitlyn, are described in their respective lore as the police of their home state, Piltover. Some years after Vi's release, the two were given Officer skins, making them resemble more modern/stereotypical police officers, complete with blue uniforms, hats and badges.
Jhin's passive is the first of it's kind in League of Legends, among his four other abilities, all of which are hodgepodges of abilities from existing Champions. Jhin doesn't gain any bonus attack speed or critical strike chance from items in matches, these stats are instead converted into attack damage, and attack speed becomes movement speed for whenever Jhin is reloading after his four-hit passive.
The initial concept for Jhin was that he was supposed to be some form of robotic bounty hunter-sniper. This concept was scrapped for a more psychotic, criminally insane persona, but the visual design went on to become his High Noon Jhin skin.
On the Howling Abyss map, player's inventories by default have the trinket slot occupied by 'Poro Snax', which can be fed to nearby Poros to make them happy. If a Braum feeds a Poro, they grow a distinct black mustache, akin to his own. Feeding a Poro with the Dragonslayer Braum skin gives Poros orange mustaches.
The name of the character Riven the Exile appears to be a subtle nod to the Myst video game franchise. Riven was the name of the second game in the Myst series and Exile was the subtitle for the third game.