Democracy Mode. No matter what Anarchy/Democracy system is used for the run, there will always be players that will chastise those who use democracy for anything positive or negative.
Lore. While Crystal has some snippets of side lore to differentiate the run from Red (as the story originally was a carbon copy of Red's rather than a continuation to Red), Emerald started the trend of people making lore before the run even started, sometimes already having the protagonist's personality made, before the events that occur on stream destroys any context what they've made. As such, people have various definitions on what constitutes "forced lore" from "genuine lore", because of the increase of branching story lines being created throughout the runs. As of Touhoumon & Moemon, it became of a recurring joke by the chat of making fun of those who insist of making a story for every game being played instead of actually playing the game and having fun, although how much they mean it is up to the viewer.
Whether runs should have lore or not anymore. The official subreddit still insist on coming up with lore based on what happens in the runs, while most people who only go to the stream have started poking fun at them over it in the latter runs. As of late, many on the stream just prefer playing the games now and enjoying the insanity that ensues, whereas the fans on the subreddit and social media tags tend to prefer crafting lore to playing.
Season 4 saw Streamer take a less active role, giving a lot of control over running the stream to an Ascended Fanboy with the username M4_Used_Rollout. Reactions to how he runs the stream have been decidedly mixed, with the primary complaint being that he's too heavy-handed (e.g. disabling the release coordinates in Randomized White 2 without telling anyone, enabling Democracy for the Azure fight in Pyrite, taking direct control of the stream in Theta Emerald EX to allow the Mach Bike puzzles, which are impossible in either system, to be traversed).
Contested Sequel: Those who experienced multiple runs have vast opinions on which run is better or worse than the previous run, whether being the run's events in question or the level of enjoyment.
Subverted for the number of viewers. Despite its constant average of 300-800 simultaneous viewers since the Nintendo DS runs and 100-200 simultaneous viewers in Season 9, with some spikes here and there, the number of unique viewers per day has been high as ever.
In terms of the run themselves, Twitch Plays Pokémon Black was this for Season 1 due to a decrease of morale after subsequent releases in its first few days and Twitch Plays Touhoumon & Moemon for Season 2 due to being similar to previous Kanto runs and its dual-input system being more tedious than enjoyable.
The middle of Season 8 was plagued with trolls who took advantage of the significantly lower fanbase than the glory days had had to stall for hours at a time, mass release party members and entire boxes, and, in Blazing Emerald, giving all the Pokémon increasingly dirty names. This led to a bunch of grimdark lore as well, with even the lighter interpretations portraying W ☹☹'' and AGGGNNV as depressed and angsty Emo Teens and the darker ones making them full Villain Protagonists (contrast with Emerald and Black in Season 1, where attempts to make A a serial killer who bumped off would-be hosts or GMYC a zealot who willingly killed his own teammates to appease the Voices were rejected by the fanbase as too edgy and hard to write lore around).
Out of all the games played in between Crystal and Emerald, MOTHER 3 is the most memorable one.
Most chat emoticons became popular because of the stream, mainly due to frequent spamming.
Fan Nickname: A lot of Pokemon have been given fan nicknames over the course of the playthroughs. Pokemon are often given unpronouncable names that are just random letters, so they are often given nicknames that are easier to remember and type. Many recieve nicknames that are based on they way their nonsensical nicknames might sound (like ZDNNNG the Skitty was named "Chairman Meow Zedong"), their powers or abilities (like Digrat, the Rattata who knew Dig and often used it at inopportune moments), or their supposed divine origin (such as Lord Helix, an Omanyte that came from the holy Helix fossil that Red looked at over and over again).
Viewership was still strong for Crystal but could never quite match Red's popularity, and it dropped off sharply during Emerald. Even when Twitch advertised the one year anniversary of the stream for Twitch Plays Pokémon Red Anniversary, the highest it got was ten thousand in its start and sharply dropped to a few thousand in a couple of hours.
Whenever someone mentions TPP, most people refer to the Red run. Someone talking about Crystal or Emerald is fairly uncommon, and a rarity for any run after that.
Eventually defied...sort of. In September and October of 2017, the subreddit held a "Survivor-style" poll series in which people voted off their least favorite run. Crystal was the last one standing, while Red exited in 7th place and Emerald was surprisingly knocked out in 21st, before any other Season 1 run.
For a lot of people, the appeal fell through after Red ended, largely due to Crystal retreading the same ground. Others stuck around longer, but largely, the fanbase is nowhere near as large as it once was. Most people who return to the stream for a long time are usually surprised the channel has lasted so long, and it has been a recurring joke for the chat to question if TPP is still a "thing" or not.
The max that Anniversary Red had was 3,500, and only during the Elite Four runs. The usual was around 500-900 players at once.
After all the jokes in the first season about doing "solo runs" because they only had one decent mon left, Vietnamese Crystal ended up actually doing a 99%-solo-run with their starter. With only a few inputs per hour, it would have taken forever to train and switch between multiple mons, so they rarely bothered using anyone other than "BEST."
Some people find the feud between the anarchists and democrats to be more entertaining than the game itself.
As of late, there are those who enjoy Twitch Plays Pokémon: Arena more than the main runs themselves, disappearing whenever the intermission ends.
Mentor Ship: Steven took Orlando in and acted as a mentor and assisted him in his tasks, and in some interpretations they became an Official Couple.
Pandering to the Base: The characterization and overarching story for most of the Red run was spontaneously born and then perpetuated via Memetic Mutation. As the novelty, and thus, the viewerbase declined, those elements began to be set (sometimes beforehand) by a tight-knit group of viewers, primarily from the TPP subreddit.
Ron the Death Eater: Bill became one to in the eyes of the Mob. While in Pokemon canon he is a friendly researcher, the Mob thinks that he is an agent of the Dome Fossil, may be behind the insanity of the protagonists, and he invented the dreaded PC storage system.
Later on in the TPP series, Bill seemed to have betrayed the Dome for his own purposes. He thus became the Big Bad of season 1.
The Scrappy: The modbots, mainly for temporarily banning a person for something that their message didn't even have, such as overuse of capitals.
Red Anniversary: The spectacular Battle Tent glitch involving a Golduck (that Abe didn't own) replacing Onix, encountering the extremely dangerous glitch Charizard 'M, and losing every Pokemon in the party and blacking out every few steps until Streamer and the game's hacker stepped in.
Touhoumon/Moemon: The daycare glitch leaving Athena with a party full of Ivysaurs whose current HP exceeded their maximum HP.
Alpha Sapphire: Nina spending an hour trapped in the air and 2.5 hours trapped in a secret base.
Colosseum and XD: Watching the news.
Crystal Anniversary: The first appearance of OLDEN and the Gainax Ending with the Unown spelling out ominous messages.
Randomized Platinum: Releasing Blaziken in Democracy.
Blazed Glazed: The flaming mountain.
Pyrite: The 36 attempts against the final boss, only succeeding in Democracy.