Pokémon Colosseum/YMMV

Series as a Whole

 * Complete Monster: Cipher is more or less built around this trope, since making Shadow Pokémon means abusing them to the ninth degree. The more Shadow Pokémon, the higher your rank and the more likely that you're an utter bastard. Big Bad Boss Evice, Dragon-in-Chief Nascour, and Mad Scientist Ein are therefore the worst of the whole lot.
 * Ein in particular deserves mention, seeing as he's the Evil Genius behind Shadow Pokemon in the first place, comes off as a cold and callous sociopath who cares nothing for life other than experimenting on it, and even wants to perfect the process of turning Pokemon into heartless killing machines just to show he can.
 * Creepy Awesome: Cipher is pure evil and the patron saints of Paranoia Fuel for the cold, calculating efficiency with which they do their work, subverting as many protection fallacies as they think they can get away with. On the other hand, said cold, calculating efficiency and genre savviness has drawn them a number of fans.
 * Crowning Music of Awesome: Miror B. in both games has great battle music. The salsa-ish beat to go with his Ludicolo team in Colosseum is fitting and popular. And the funky disco of his XD theme can get stuck in your head for days. Having two such popular themes contributes to Miror B.'s status as an Ensemble Darkhorse.
 * There are quite a few epic battle themes in this game. The Cipher admin theme and 's theme stand out in particular.
 * Draco in Leather Pants: Venus and Lovrina are this in-universe, each having in-game fan clubs devoted to them.
 * Ensemble Darkhorse: Miror B. in both games.
 * Wes is also one of the most popular Player Characters in the entire series, probably because he's a Badass Longcoat Anti-Hero Defector From Decadence whose introduction scene is one the biggest Crowning Moment of Awesome in the entire series.
 * Hell, pretty much every character in the entire first game is a darkhorse. Rui, Ein, Venus, Nascour and Dakim all have their followings; the only character who doesn't is.
 * Actually, even
 * As for XD, Lovrina, Eldes, and Ardos all have their fair share of fans as well.
 * Evil Is Sexy: Ein, Venus, and Lovrina. All of them evil to varying degrees but all of them so good looking.
 * Mis Blamed: Game Freak didn't work on these games; although a Nintendo and Pokémon-company owned franchise did.
 * Nightmare Fuel: Orre's the only region to have its own section.
 * They Changed It, Now It Sucks: Fans were asking for a more plot-driven and Darker and Edgier take on the series since Gen I. Colosseum comes out and what's it criticised for? "It's not like Pokémon Ruby and Sapphire". They were not nice to Colosseum... however they lightened up around time for Mystery Dungeon and Ranger, and Colosseum gets a lot more love nowadays for its innovation.

Colosseum

 * Accidental Innuendo: A construction worker in the Pyrite Hotel says "Apparently some rich fellow ordered the colosseum built. I'm amazingly stiff."
 * Breather Boss: For being the boss of Team Snagem, Gonzap isn't all that hard of a guy to battle, especially compared to the Cipher Admin rematches you had before him. While he loves having his Pokémon use Earthquake like Dakim, he isn't able to protect his other Pokémon from friendly fire, so he ends up crippling his team while his Pokémon can be easily picked off. The only truly annoying part of his fight is trying to catch his Shadow Skarmory which is particularly obnoxious, but it's still more annoying and time consuming rather than truly difficult.
 * Complete Monster: Ein. In a team full of bastards who are dedicated to turning Pokémon into vicious killing-machines, Ein is the worst of the bunch as he is the one who created the process in the first place, and seeks to perfect the process.
 * Nascour and Evice could also count, since they are fully complicit in the Shadow Pokémon development process and oversee every abominable action in the game.
 * Ensemble Darkhorse: This game introduced the hilariously eccentric disco-maniac Miror B. And by association, Ludicolo became a lot more popular since its hilariously awesome Mexican pineapple duck design had a lot more attention called to it than in the mainstream Hoenn games.
 * Thanks to a certain Let's Player, the Shadow Misdreavus you can snag has become ridiculously popular.
 * Goddamned Boss: Unlike almost every other high-ranking member of Cipher, Venus's Pokémon don't make use of devastating attacks and aren't particularly dangerous by themselves. However, she LOVES to spam Attract which make it to where Pokémon of the opposite gender are very unlikely to attack each turn, and ALL of her Pokémon know it. She also has various other moves like Thunder Wave, Confuse Ray, and Curse (The Ghost variant) to stack on top of that to annoy you to death.
 * There's also Justy of the Pre Gym whose main strategy is to spam Double Team. Over. And. OVER. Again. Add in the fact that he also uses Sandstorm to chip away at your Pokémon's health while his Pokémon get their bulk increased (or even worse, their accuracy boosted EVEN MORE), and you have a painfully obnoxious boss battle on your hands that is an absolutely miserable experience all around. On the bright side though, you get the Double Team TM for beating him, meaning that YOU get to use this strategy against your foes...
 * Miror B. isn't hard per se, but his Ludicolo team is still annoying to take down. They're all fully evolved Pokémon in a portion where you mostly fight non-evolved/not fully evolved Pokémon that boost great defensive stats and can gradually recover health with Rain Dance + Rain Dish and Leech Seed. There' also the fact that thanks to their great Water/Grass typing, they're weak to pretty much nothing up to this point, leaving you to smack them with the strongest attacks you have.
 * Good Bad Bugs: Colosseum allows you to use any Ball an infinite number of times by using it on your first mon's turn and switching your item list around in the second - and yes, this includes the Master Ball. XD fixed this.
 * Moral Event Horizon: Dr. Ein crosses this just by inventing the Shadow Pokemon system (without a shred of remorse, and actually with a desire to improve it), and  just by leading the whole operation. Particularly
 * Play the Game Skip the Story: Fans and former fans demanded a more plot-driven Pokémon game or for a Darker and Edgier entry to the series. They get Colosseum and...the responses are either "WTF where are the wilds?" "Why is this not like Pokemon Red or Blue?", "Shadow Pokémon? WTF are they babbling on about I wanna EV train!", "Double Battles? I HATE Double Battles!", while the Darker and Edgier stuff was mostly completely ignored by the "Pokémon is kiddy" age-ghetto types.
 * Although some people actually did pay attention. This is like the Ensemble Darkhorse of games in the franchise, after all.
 * Scrappy Mechanic: Shadow Rush in Colosseum inflicted recoil damage, which the computer tended to use to deny a Snag by forcing a self KO (Which is really annoying with Colosseum's use of Save Points and leads to much back tracking). This is fixed in XD. Now there are more Shadow moves than Shadow Rush and only Shadow Half (reduces the HP of all Pokémon on the field by half) and Shadow End (deal great damage but reduces the user's HP by half) have recoil (both appear only on end-game snag targets), but they have the same lethality as False Swipe, which benefits the player.
 * Hyper Mode in all its lose a turn glory - especially if said Pokemon is low on health and likely to get K Od before being able to take the opponent down first.
 * Can be seen as a blessing if you're interested in purifying all pokemon quickly; the pokemon at a cost of a lost turn will also gain happiness points, reducing the amount of time needed to purify it.
 * That One Boss: Applicable to any and all bosses who own Legendary or third-stage/uber Pokémon. However, a rather early game, and very maddening example, is Dakim, who uses a brutally effective strategy to utterly destroy you: One Pokémon Protects (making itself immune to damage), the other uses Earthquake. Next turn, the roles switch. So you either eat Earthquakes until they run out of PP for Protect, or use somthing like Encore to screw their strategy up. When you take into account that Dakim has Entei, and Entei is Fire-type, which takes supereffective damage from Ground-type attacks, which is what Earthquake is, well...
 * Ein as well, given how the guy's team relies on Rain Dance, which boosts the Water moves of his, well, Water type Pokémon to insane levels while his others can use the powerful Thunder now with perfect accuracy. He's also a big fan of confusing and paralyzing your Pokémon so they can't do anything while he absolutely tears into you.
 * The final boss could possibly give Ghetsis  and Cynthia a run for their money when it comes to being the franchise's hardest final boss. All of his Pokémon save for his Slowking pack fantastic attacking stats as well as moves like Bulk Up and Swords Dance to become even more powerful, and he also has them all above level sixty when your Pokémon are likely to be in the low-mid fifties. Even worse, he has a Scizor who WILL Baton Pass Swords Dances onto his other Pokémon, giving them a huge attack boos right out the gate. And if his Slowking Skill Swaps with Slaking to remove its Truant ability? Kiss your ass goodbye.
 * The Woobie: Silva is a minor example of this. The poor guy tries his best to help Wes and Rui out with stopping Team Cipher, but he constantly gets beaten up/taken hostage/otherwise humiliated for his efforts.

XD

 * It's the Same, Now It Sucks: Did the game have to re-use so much from Colosseum?
 * I Thought It Meant: No, the name of the game doesn't mean "Pokemon, LOL".
 * Moral Event Horizon: Cipher as a whole crosses it in the first scene (as if they weren't on the other side of the line already) with the destruction of the S.S. Libra, which is confirmed to kill several people.
 * Individually, we have Snattle's imprisonment of an entire town's population (apparently using violence no less), Lovrina's corruption of Shadow Lugia, and Ardos attempting to get Michael and everyone else within the area killed.
 * Paranoia Fuel: In XD, Cipher Peons have a tendency to drop down from the ceiling when you least expect it. There's also one time where you get on an elevator alone, and you come out of said elevator with a Peon behind you.
 * Replacement Scrappy: Michael.
 * The Scrappy: Michael's little sister Jovi. Big time.
 * Scrappy Mechanic: Poke Spots defeated the entire point of Shadow Pokemon and Orre, and gave rubbish Pokemon anyway.
 * That One Boss: Snattle's 2nd fight is brutal on its own, with his Shadow Starmie being an insane sweeper and being fought a long way away from a healing machine on either end, but you fight the smartest grunt in the franchise right afterwards.
 * They Changed It, Now It Sucks: The things they didn't keep the same rubbed some fans the wrong way, particularly changing Orre into a much more habitable place, thus losing its "edge."