Why a bad argument? It proves the achievement is almost impossibly hard but still doable. I think it's totally fair to give an exclusive badge only to "Player X" because they were the only one who achieved it.
I think there are a line between excessively hard achievements and excessively artificial achievements that should be drawn. Achievements like "complete the game in one session at level 1 without equipment" may fit on a bonus set depending on the game. But achievements like Where's My Super Suit (100) are part of the game and should be part of the core set. Whoever thinks it's too hard should simply leave the game at 99% and go to the next set.

I agree with the Mario RPG one. I have said before, I have no problem with cheevos that make you experience everything the game has to offer. If there's a secret or cool item you can get that you would miss otherwise, having an achievement is a great incentive to do that. It's why I gave so much praise to the Sonic Adventure set, because I've been playing the game since I was a kid and didn't know about Big's secret area in the Hot Shelter.

My issue is with ridiculous challenges that make you play the game it was never intended to. Look at the Sonic Heroes Chaos Emerald Challenge achievements, for one. A score based achievement when the goal is to do it quickly? On top of the abysmal glitchy controls? I'm not the only one who's complained about that either! Or say, the "beat level with only x character" in Heroes as well. I had to abuse the physics and crappy wall collision in unreliable ways to get one of those. Just doesn't seem natural or fun at all. The Kirby's Dream Land achievement with no damage Kaboola was also a sore one. You have to pause buffer and be literally frame perfect on top of that to get it done due to how spammy and unpredictable it is. Yes, they are doable, but by that logic, EVERYTHING is doable if you just think about it or watch some streamer do it.

I'm just most upset about devs clearly not knowing the game and making cheevos around it because they looked up literal world records in score and time categories. Almost like half of the games I've tried have had this issue as indicated by comments by others. Were they changed? Sometimes, and only sometimes. There needs to be more care put into this stuff, and I don't know if it's specific to platformers or what, but it's ridiculously common for what it is.

I got this achievement last month (i think) and is not hard but frustating, mario doesn't have a good animation like paper mario or the gba/ds rpg games and this is the hard part (at least for me) feels like a brick and just for blinking you can lost and to be honest if losing at 90 jumps for sure the player will be blaming the achievement or developer but i think this is normal is just the moment.

But talking in general i don't think retroachievement are beyond my skill or anybody else, is more if you is having fun enough to praticing and getting, there is no one who get a hard achievement in your first try or in little time, I do what I like to do and not what i don't like.

Just play and have fun, i think some people have 2 profiles, in 1 they let 100% with sets they know they can do this and the other they play what they don't can do it.

Glad to hear we are at same page. Definitely there are artificial achievements that maybe shouldn't be on a core set, however sometimes the judgement about this is pretty subjective and that's the reason why those changes are voted only by the developers. Unfortunately there's no other option at the moment other than become a developer and propose the changes we consider fair, like moving achievements to bonus or simply demoting.
Of course that sounds like too much effort for some people, but may be a good reason to become more engaged and participative on the community.

ElectricAngel: I think our expectations are different, because official achievements aren't even consistent in difficulty from game to game. If anything, RetroAchievements seems to have more rules, even if they're slowly enforced. And sometimes bullshit is in the game itself, like the items from jump rope and speed running Final Fantasy IX, so I'm just used to knowing what's not for me and glad enough that not earning a retro achievement won't keep me from in-game unlockables.

I also don't enjoy hard games in the first place (had enough of that as a Genesis kid), so I'm probably not running into the worst examples. I have ran into some that I don't like, but me not liking them doesn't make them BS. There are some people who genuinely enjoy challenge runs, etc., and I know that because I've seen all kinds of challenge walkthroughs and mods to increase difficulty since I was a kid. That 2-arrow Shadow of the Colossus achievement doesn't sound like one I'd enjoy or spend more than a couple of tries on if any, but even that isn't out of line with some official achievements I've seen. I think there was one in Bioshock Infinite that made you kill a certain enemy by only hitting its heart (which had to be shot multiple times). And while "x is also BS" isn't much of an excuse, I really can't expect volunteers to do better.

I just started the first Wild Arms and saw in the topic that a few achievements that were deemed too grindy were actually removed. But even then, there were some people who had actually done it (but I don't think this site should be encouraging people to straight up waste their time when there are so many games). I'm not sure what you mean about achievements that require hacks, since I thought that would prevent hardcore achievements? I also haven't ran into clinging onto broken versions of a game, but that does sound unfortunate.

Not to say every set is flawless, but it just seems to me people panic very easily about speedrun achievements. The hard part of speedrunning is the precise, complex glitches they pull off back to back. Personally I've only seen sets that require some routing effort, which is something that's usually already done for you. The perception of having to be a full time speedrunner to get decent at a single level is holding people back from something that's honestly not that hard.

What ElectricAngel is saying about the Sonic heroes achievements is something I can imagine being more of a legitimate problem rather than a genuine skill issue. Haven't tried the set out just yet, though I will someday. But achievements that don't really take into account what kind of problems the game has built in, or just flat out goes against what the game was designed around, are where potential problems pop up.

So if there's like, provable bad design, the community can decide on a potential change if it bothers enough people. But something being subjectively too difficult, it's hard to get a consensus if there's nothing beyond a few people saying it's too hard. A low players earned percentage doesn't necessarily act as proof of something being too hard either. It's incredibly common even outside of this site for the percentage earned to drop hard and fast. 96% of people got 1 star in mario 64, but only 52% got 8 stars. Or how about the achievement for beating king bob-omb without being damaged, which only 31% of people have done. It's not too hard for 70% of people to do, but even just finishing games seems to be niche let alone doing minor extra stuff, LET ALONE anything actually remotely challenging.

As long as there's a quick way to retry the challenge, asking you to get good at a single segment is just not too difficult for a main set. If you look at bonus sets, a lot of the things people want put in there would be laughably easy compared to what kind of things actually get put in subsets. I'm not trying to say "git gud" But I do think people scare themselves out of doing things they're fully capable of accomplishing.

@Hotscrock

I don't feel that the game providing a reward for the player is enough justification for an achievement being in the core set. For example, Super Smash Bros. Melee gives you a unique, permanently-logged notification for completing one million VS. matches—which requires about a third of a year of playtime—but I struggle to imagine anyone arguing for its inclusion in the core set when that game eventually gets one. Would you?

There's an implicit understanding of a balance between developmental significance and player effort for something to be valuable enough to warrant recognition in the core set. An additional line of text—which would take a developer thirty seconds to add—coupled with an absurd amount of effort to attain clearly doesn't meet that threshold. I'd argue that something like the Super Suit doesn't either: an item ID and a couple of fields is a developmental afterthought, a message included in the game just because they could, much like the message for one million VS. matches.

AriMaeda The 1 million vs battle achievement is a common sense that would fall under excessive grinding unwelcome concept different from the SMRPG one. But still those examples are understandable. What is not understandable is complaints about any damageless or time attack achievement.