The Mexican Spanish dub is not a slouch in this department either, since it features many younger and veteran voice actors as well.
The Spaniard dub features a great number of Madrid based actors, both veterans, newcomers and newcomers that had become veterans; that continues to grow with each champion update and release. Alfonso Vallés is the only actor from Barcelona in the game (he voiced Gangplank's second visual update) which makes the game's VA cast even more all star.
The Brazilian Portuguese cast uses most of São Paulo and Rio de Janeiro's top voice actors, as well as a few rising stars.
Banned in China: Similar to the issue with the Forsaken in World of Warcraft, Karthus was redesigned from a skull-faced lich to a withered, shadow-wrapped figure for the Chinese art, due to taboos about representations of skeletons in media. The only skins that keep their skull-faced appearances are his Grim Reaper skin (likely because it represents the more abstract personification of death) and his Pentakill skin (for reasons unknown).
Beam Me Up, Scotty!: Contrary to Memetic Mutation, Garen doesn't shout "DEMACIA!" when using Judgement (his signature Spin Attack). That's a separate skill, Courage, but because Courage is usually used in combo with Judgement, it comes across as the most widely known case.
Celebrity Voice Actor: Nigerian-American rapper Umar Ibrahim, better known as Thutmose, serves not only as a musical collaborator representing Ekko as part of True Damage, he also provides the skin's in-game voiceover.
Much of the content for the 2020 Spirit Blossom event was leaked at least a month before official release, with screenshots and documents confirming skins for Ahri, Cassiopeia, Kindred, and Riven, as well as prematurely announcing Yone as the next new champion (who was additionally verified thanks to datamining Spirit Blossom Thresh's voice lines). While Riot's plan was to release the content on the set schedule shown in the game's client, they did quietly add some cosmetic assets (icons and emotes) onto the PBE based on several of these leaks, further confirming them.
After Seraphine's K/DA Character Blog began but before she was officially announced as a champion, her kit was prematurely discovered through datamining in Wild Rift during its closed beta, the first concrete connection between her and League of Legends.
Lee Sin was a very early champion concept (you can see him in early trailers for the game), but the character was canceled due to his design not being seen fantastic enough. There were rumors of him being put back into development floating around for a good long while, especially after champion designs became less fantastic, until late March 2011 where he was announced once more, with a new model, skillset, and name.
Ao Shin was first announced back in 2013 and slated to be released before Lucian and Jinx. Then the design team had quite a hard time animating a serpentine figure, and he was delayed. Then the gameplay mechanics team started bashing their heads over and over again trying to design his ability kit, going as far as drafting and scrapping multiple different kits altogether. By 2015, Ao Shin had already acquired the status of the champion that will never, ever be released. The design team eventually gave up, changed his entire theme and ability kit completely, and was finally released in 2016 as Aurelion Sol. In 2020, Ao Shin himself was sort-of added to the game as a skin for Aurelion Sol and as a Little Legend for use in Teamfight Tactics.
It is worth noting that the lead developers of both Dota 2 and League of Legends were the lead developers of Defense of the Ancients. Guinsoo, the first lead developer, was hired by Riot Games; IceFrog, a later developer who took the game after Guinsoo resigned, was hired by Valve.
A few days before Wukong's first preview blurb, competing game Heroes of Newerth announced its new champion: the Monkey King. Technically HoN created concept art first, but didn't do anything with it until rumours about a Monkey King in LoL surfaced. Needless to say, accusations of copying were flung from both ends despite the character clearly being a reference to Sun Wukong from Journey to the West.
I Knew It!: In 2020, Riot teased one of their new champions as a masked assassin who refused to die, and was already present in the lore. Thanks to the subtle clues, several fans suspected it was Yone long before the above-mentioned leaks confirmed it.
In Memoriam: The "Total Biscuit of Rejuvenation" item was introduced in 2012 as a result of and named after John "TotalBiscuit" Bain. After Bain's passing from a several year-long battle with cancer in 2018, the item has since been renamed the "Total Biscuit of Everlasting Will".
Model Dissonance: In-game character models, especially later on, are designed to look good for the sole isometric/aerial camera angle for gameplay. As such, some can look a little weird when viewed at more "normal" angles from in-engine champion trailers and spotlights, popular examples being Irelia'senormous hips and Akali's hands.
Now Which One Was That Voice?: Due to the game's non-union development and constantly-updating nature, Riot Games had a longstanding policy of not disclosing their voice actors unless the actors themselves publicly reveal themselves first. While the rule was rescinded in early 2019 and Riot has since become more open in crediting newer actors, the identities of those behind many older champions remain unknown.
It's pretty much a given that if Riot reworks a champion and their lore to an especially drastic degree (among the biggest examples being Sion, Poppy, and Urgot), they probably regret their prior incarnation by quite a bit. When asked about old Mordekaiser's lore in light of his upcoming 2019 relaunch:
Riot Xenogenic: Imagine a movie where people find a lost tomb, and that tomb is cursed, and everyone who comes out of it and talks about it dies. Let's just say: it's better if we don't talk about Morde's old scripts.
The "Dark Horses", strategies advertised by Riot to use champions in unusual ways, appears to be this for Riot, as they gave up on the concept after making only 6 and now no longer talk about it anymore aside from as a source of Self-Deprecating Humor during April Fool's of 2016. The first one, Support Brand, was the only success, as Brand's high internal damage and single-target stun allows him to function as a poke support in a similar style to Lux and Zyra. Their next go, Jungle Irelia, was a complete flop that drew mockery from the fanbase, as Irelia clears the jungle very slowly and requires too much gold to function from it unless she happens to get off a few successful ganks early on. They tried to play it safe with their next 4 examples, but solo-lane Jarvan, top-lane Urgot, support Nautilus, and jungle Gragas were already things that were being done with regularity, earning Riot further mockery.
Sewn Chaos Amumu and Blitzcrank made it onto the PBE and were almost ready to go, but after negative fan feedback that Riot agreed with, the skins were cancelled before they could be properly sold live. Riot seems to view them as this, as their Dummied Out skin description reads "Due to their low quality and uglyness, these toys are destined to remain in the toy trash bin of unwantedness."
In July 2019, Lee Sin's voiceover by Vic Mignogna was replaced with a new one by Feodor Chin. While Riot hasn't given an official statement as to why (Lee Sin received no other accompanying visual update), this was generally seen as a response to the sexual harassment allegations against Mignogna from earlier in the year.
With the music of Pentakill, the singers behind the champions are in constant rotation: Jørn Lande provides Karthus' voice in "Lightbringer" and "Mortal Reminder", while "Deathfire Grasp" and "Last Whisper" are performed by ZP Theart, and "Infinity Edge" and "Rapidfire Cannon" are voiced by Per Johannson.
Similarly, K/DA's vocal cast has some variable vocal casting. While they're pretty consistent with Miyeon and Soyeon as Ahri and Akali, Evelynn has been performed by Madison Beer and Bea Miller, and Kai'Sa by Jaira Burns and Wolftyla.
In the Japanese dub:
Naomi Kusumi is Tahm Kench's new voice actor after Unshō Ishizuka's death in 2018.
According to this Ask Riot post, Rammus' extreme laconicity came about because of the attempt to replace his old voice track. The new one was too awful and sounded 'pretty hillbilly'. Not even wanting their own internal team to hear it, the devs recorded his current voice in a conference room in the space of fifteen minutes. They meant to replace it but never got the chance, and Rammus' one-word dialogue went on to be the defining point of his character and spawned the 'Ok' meme.
This Ask Riot revealed several development Working Titles for several champions over the years, several of which interestingly became their official subtitles (including Elise, Vi, Thresh, Illaoi, and Taliyah).
Promoted Fanboy: Even prior to being cast as the Japanese voices of Heimerdinger, Veigar, and Ziggs, Natsuki Hanae was a big fan of the game.
Reality Subtext: Subverted, but worth mentioning; the champion Tryndamere shares the handle of Riot co-founder Marc Merrill, and it was initially believed that his marriage to Ashe was based off the fact Merrill's wife is named Ashley. This was debunked by Merrill himself as the creative team had no knowledge of this fact, meaning it was just a massive coincidence.
In terms of default voiceovers, Lisa Lindsley has voiced Soraka before and after her VGU, same with Doug Boyd voicing Twitch, Carrie Keranen voicing Lux, and Melissa Hutchison voicing Ashe.
This doesn't seem to be as much of a problem for Legendary skins, with many sharing the same voice actors as the original, regardless of the developmental time gap. Some came back within a couple of years like Chuck Kourouklis for Dunkmaster Darius, Sarah Williams for Star Guardian Jinx, Liam O'Brien for Nightbringer Yasuo, and some returned after significantly longer gaps, including Laura Post for Star Guardian Ahri, Kirsten Potter for Pulsefire Caitlyn, Carrie Keranen for Elementalist Lux, Cristina Vee for Dawnbringer Riven, Melissa Hutchison for PROJECT: Ashe and High Noon Ashe (and later came back for the vanilla version's general update), Vic Mignogna for God Fist Lee Sin (both have been replaced come 2019), and Kyle Hebert for Pulsefire Ezreal (both his 2012 and 2017 recordings, though he was replaced for Ezreal's global 2018 VGU).
Riot then released this "spotlight". Game Breaking... no, Game DESTROYING power, a "blurry" screen debuff, and the ability to kill members of your own team who defect to the other side. They released an actual spotlight video shortly after.
Their 2012 prank (a really bad 3D mode) was obvious (made even more so by the Urf cameo at the end), but nonetheless hilarious. Incidentally, they've actually named April Fool's Day "Urf Day."
Riot announced early 2019 that after a 50/50 split of new champions to visual/gameplay champion updates throughout 2018, they would be greatly slowing down on the VGUs in large part due to the champions' original fans constantly crying foul of "They Changed It, Now It Sucks!", even if the reworks are hugely-requested and overall well-received. As a tradeoff to this, however, Riot has also since become more careful in handling these relaunches, being more vocal and public about their development processes and taking fan feedback into greater account.
Between 2019-2020, Riot shut down the Community Events featureson the EU and NA clients, a tool originally meant for small organizers to run online tournaments, offering tangible prizes like RP and codes for the Triumphant Ryze skin (which is the only way to obtain the skin). The feature was removed once it became clear that it was a massive target for exploits, where players would use use dummy tournaments to farm for RP and accounts with the Ryze skin code, both of which could be sold illicitly.
In a 2020 Twitter thread, former writer Devon "Runaan" Giehl explained that she wrote Twisted Fate and Graves as a gay pair, a decision which was originally met with much hostility within Riot's offices, but years following her departure was subsequently revisited and repeatedly teased, much to her dismay.