These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Badass Decay: When Tiger first shows up, he's serving up The Worf Effect like nobody's business (even to Asakura), but as time goes on and his real character comes through, he proves incapable of winning any fight at all.
Epileptic Trees: Odin was the subject of a lot of them due to his importance in the plot, the lack of direct explanation as to who or what he was (until the final episode) and certain promotional scans (such as one with him holding all three Survive Cards in his Gold Visor).
Also Odin himself, able to beat a Rider in Survive form. Possibly invoked, because Shiro is the one controlling him and only brings him in to eliminate those who oppose him.
Hilarious in Hindsight: One hallmark of Kamen Rider and all Toku in general is the "Blind Idiot" Translation subtitles on bootleg Hongkong DVDs, so much that some characters get new names. Goro in particular keeps getting called 'Inagaki', presumably because he shares the pet name 'Goro-chan' with Inagaki Goro of the immensely popular boyband SMAP. Fast forward 6 years to 2009, and the real Inagaki Goro lands the role of (the non-canon) Kamen Rider G.
In a similar vein, Ren gets called 'Len' or 'Lian' a lot in the early eps of the bootleg DVDs. Kamen Rider Dragon Knight picked Len eventually.
Also of note is how Asakura's name was completely and senselessly altered to "Miyako".
Perhaps the funniest bad translation is when Zolda summons his giant side-held cannon. His visor calls out, "Shoot Vent!" The subtitle for that line? "Jet Plane Landing!" Well, the cannon's *sorta* jetplane shaped if you squint...
Even worse is that the Visors are already in English...
Hollywood Homely: Asakura looks WAY too healthy and clean for somebody that's been homeless since childhood
Moral Event Horizon: Sudoh firmly cements his villainy after taking advantage of Shinji's trust and getting information on Ren, he sicks Volcancer on Ren. Later he revealed to have crossed it before he ever appeared given that he routinely sicked Volcancer on anybody he didn't like.
Jun already showed himself to a bastard, but he managed to one up himself when he planned to use ORE journal to set up a nation wide version of his deranged game that drove people to murder each other.
Asakura manages to cram in a lot even for his prominence in the series:
He committed a murder off-screen because the person in question annoyed him.
Lies about having tried to save his little brother and pretends to care about him so he can lure him out and kill him.
Toujo crosses it when he kills Kagawa, believing that sacrifices those closest to him made a hero, and then crosses it again when he tries to kill Sano, after Sano had taken him and been so kind to him.
Narm: Verde's Final Vent is one of the nastiest: with his chameleon monster's tongue acting as a bungee cord, he drops in on his opponent, grabbing him upside down, then bungees back up, flipping around twice before SMASHING his opponent head first into the concrete. Then the dust clears and we see the victim's legs still sticking into the air for a bit before toppling over. ...Yeah.
Paranoia Fuel: Behind every reflective surface (Mirrors, windows, any body of water, YOUR FRICKING COMPUTER SCREEN) is a monster...wait, I mean an army of monsters that is just waiting to have you for dinner. They will pull you through the portal into the Mirror World, and kill you, leaving no trace behind and making it impossible for anyone to figure out how you were killed. If by some fluke you avoid the initial attack, they will not just try for someone else. They will keep hunting YOU down specifically until they get you. Also, the Mirror World is very hostile to those not native to it, and if you are there for too long, you will dissolve and die anyway (if you haven't already been eaten). Pleasant Dreams.
The Woobie: Yui. Let's count the ways, shall we? She and her brother spend their early childhood locked up in their home by their own parents, with nothing but drawing and a not-so-imaginary world to comfort them. Then, she suddenly dies at age seven, and is replaced by her Mirror World self in her brother's Deal with the Devil. Following their parents' deaths, she and Shirou are forcibly separated. Twelve years later she finds out that she's not even real, she's only living on borrowed time and will disappear forever once she turns twenty, and that her brother is perfectly willing to manipulate twelve people - two of which are her closest friends - into killing each other in his mad scheme to save her. And that her drawings with her brother are what became the Mirror Monsters that are snatching people away and devouring them in seconds. Jesus.
Oh, it gets better. She gets to find all this out by being targeted for death by those who've worked it out, snatched by monsters, and finding herself starting to disintegrate at times. And it can all only be settled by convincing her brother to let her death stick. The final scenes make it clear that to the world, Yui died long ago and stayed that way. (Her grandmother is all alone in the tea-house, and there's a picture of Shiro and Yui as kids.)