Here's a list just off the top of my head, in no particular order. MASSIVE spoilers ahead.
-Wheeljack keeps making party drugs. This is not only accepted but wholly encouraged by the Autobots. He's made the bot equivalent to cocaine so strong it made grimlock physically unable to stop himself from running around the ship at mach 5. This was the basis for an entire episode. He's also made patches that give you a direct link to the Allspark that he passed out at a party specifically to get everyone as fucked up as physically possible. I cannot overemphasize that Optimus make no effort to stop this until things turn destructive on both occasions.
-Soundwave and Shockwave completely fucking hate each other and have a whole rivalry trying to be a better and more useful follower for Megatron than each other.
-Soundwave is a fucking memelord who will play clown music or dramatic riffs to dunk on people from the soundboard he has built into his hardware.
-theres a sort of liminal dimension referred to as Unspace that you can get stuck in and if you are there for too long you will straight up disintegrate. We see this happen to the entire crew aboard the arc from different timelines several times while the main timeline crew we follow tries to escape this fate, thus dooming dozens of other timelines.
-Cheetor is basically Allspark Jesus, and he's tired of all the fighting, so he tries to have Optimus and Megatron settle their differences once and for all. The chosen method for this was making them both play the Newlywed Game. They were both terrible at it, the MegOp Divorce agenda is alive and well.
-the Quintessons invade Cybertron and stick the entire population into a simulation a la The Matrix, which slowly drains their life force until they die. This kills countless unnamed Cybertronians, both Autobot and Decepticon, as well as Hound, who does not get to appear on screen.
-the Quintessons also catch Starscream, rip his face off, and modify him into an Eldritch tentacle beast with his brain attached to two other aliens, and then appoint that amalgamation as the judge that decides the fate of the universe in regards to whether they exterminate all life within it.
-Shockwave commits suicide for Megatron's approval. He launches his spark straight into the Allspark to taint it specifically as a last desperate fuck you to the autobots.
-Soundwave acquired laserbeak by just kind of grabbing a random bird out of the sky.
-Soundblaster is an ex-decepticon that left out of shame. That shame being Soundwave beating his ass in a beatboxing competition so fuckin hard he couldn't show his face around his faction anymore.
-The autobots keep starscream captive and try to get him to take a therapy session with the Arc's AI, and he starts out willing to actually give it a shot but said AI is kind of Stupid and screamer ends up tricking him into letting him escape through an air vent to go wreak havoc instead.
-Starscream also starts a suicide cult with the other Seekers, gains control of Vector Sigma and the Allspark, has the seekers forfeit their sparks to him, thus resulting in a cosmically powered Starscream. He uses that power to "remake" his followers into scraplets that he refers to as, with nothing but love in his tone, his "children."
-Shockwave and Wheeljack are shown to be ex lab partners. Shockwave has an army of drones that look exactly like his altmode that Wheeljack helped program. They are programmed to be able to break out into a coordinated dance number at any given time. Originally this was just to make Wheeljack laugh. Shockwave kept that function in throughout the entire war and initiates it the second there's a truce and Wheeljack asks to see it again.
-Shockwave kidnaps Wheeljack at one point for Science Under Duress purposes and Wheeljack is too invested in all the sweet fuckin tech Shockwave's been making while they were apart to really care that he's being held against his will, and then proceeds to escape without too much issue because he knows Shockwave well enough to know exactly how to disable everything.
-Bumblebee distracts the Decepticons by running in front of their surveillance cameras and shaking his ass in the most underwhelming way imaginable.
-Grimlock is only stupid when he's in his altmode because it takes a lot of power to sustain and he has to sacrifice some of his higher brain functions to keep it manageable. In robot mode he talks like he went to an Ivy League college and knows what champagne tastes like. He throws upscale parties every chance he gets.
-Grimlock also helped start an anticapitalist revolution with Bumblebee when he found an underground society of insect transformers that had a rigid caste system. This was within moments of finding out that the ultra wealthy were hoarding the limited energon reserves for themselves. Grimlock is a comrade and he does not fuck around.
-Skybyte is here and he sounds like Skeletor.
-Windblade and Slipstream are nemeses and somehow it's even more toxic yuri coded than Arcee and airachnid in tfp.
-speaking of Arcee, she's besties with Grimlock. They at one point have a physical fight over who gets to die to protect the other.
-hot rod and soundwave are forced to share leadership over the team of bots and cons that escaped the quintessons' simulation and it's packed with so much homoerotic tension its unreal.
-Maccadam is some kind of lovecraftian war machine that can unfold himself into a whole armory whenever he feels like it. We have no idea what his whole altmode looks like, all we see are the ominous shadows of the weapons on the walls. He uses this specifically as a threat to keep anyone from fighting in his bar bc he's insistent it remain neutral ground. He also can kinda just. See into the future. And casually drops prophecies that get written off as spoonerisms until they turn out to be relevant.
-Optimus Prime has horrific social anxiety that he can kind of power through when he's in a crisis, but the second things are chill and he has to give a speech at a party or something he simply does not know how to function.
-the entire planet of Velocitron gets taken over by cosmic rust and everyone inhabiting it that couldn't escape in time was killed horrifically.
-cosmos is a girl and she hangs out with a dude named Meteorfire who is, for all intents and purposes, just robot Steve Irwin.
-Astrotrain keeps closing doors in people's faces for the funny
-Megatron is killed by a version of himself from an alternate universe that went nuts and starting creating a master race of perfect Decepticons to inhabit Cybertron. Said perfect Decepticons were carbon copies of idw Tarn in all but personality.
-Acidstorm is canonically genderfluid and keeps switching between male and female seeker frames whenever they feel like it
-Kup, who had not been in the show at all until this point, decides to show up and narrate an entire episode like hes giving a political speech.
And, the infamous one we all know and love
-Megatron is a twitch streamer and he livestreams Starscream's fucking funeral. The chat has custom Decepticon emotes.
