Record progress and skill milestones. Prior to achievements Cogmind already included a couple such systems in the form of lore and item gallery completion rates, and aside from their reference value they've shown to be useful among players when it comes to keeping track of their own long-term progress, and also measuring their progress versus other players in the community. Achievements provide yet another metric for both personal advancement and to compare against other players.

Recognize special accomplishments. Some interesting aspects of a run that a player might accomplish in the course of normal play under certain circumstances may go unnoticed or forgotten in the long term. Achievements can offer formal recognition of these accomplishments, like Shocking Conclusion, earned after corrupting 50 hostiles (something that combat players with a heavy EM focus might manage in a single run).

Create unique meta challenges. Unlike achievements that recognize existing milestones or likely (if situational) accomplishments, another type of achievement can actually suggest new goals outside the normal scope of gameplay. For example the Giant Slayer achievement challenges the player to take down five Behemoths. It's fairly rare for players to even encounter this many in a single run, much less attack them (since they can be troublesome and are often best avoided when possible). So this isn't the kind of achievement one might incidentally earn, but instead means actively hunting them down, requiring a different style and possibly a specialized build. Although having achievements at all increases replayability (as a kind of "collectible" like the lore and gallery), meta challenges are one of the best categories in that regard because they essentially expand the scope of the game.

Teach players about the world or mechanics. At the most basic level, achievements can be an alternative indirect method of helping players learn. Lots of games have these, perhaps because many players are blind to tutorials or help messages but pay a lot more attention when it comes to achievements! Still, although I added quite a few of these there isn't a lot of overlap with Cogmind's dedicated tutorial messages. For example there aren't any "achievements" for basic UI functionality (which the tutorial messages cover), but instead we have achievements for some mechanics worth highlighting which don't otherwise have a tutorial, e.g. Hehehe ("Reprogram a trap."), or useful tips like Short-term Sacrifices ("Escape a Stasis Trap with help from an explosion."). Loot Pinata ("Destroy a Hauler.") was added because I've heard of players going for a while before realizing Haulers are a pretty good source of decent parts, or at least a source of spares, so achievements like these are aimed mainly at the players interested in actively seeking out achievements, where these are low-hanging fruit and also teach something in the process.

Hint at some things possible in the game. Achievements can be used as a way to tease content or features that players may not have early or easy access to, kind of as an incentive to keep exploring further. "Subspace Traveler" is simply described as "Find a way to teleport"--most players still don't even know this is a thing in Cogmind :). Then there's "WMD" ("Destroy 100 robots in a single turn."), suggesting that it's possible to wield some pretty devastating firepower. Similarly, only one plot-related achievement was intentionally left unhidden, "Origins," which is described as "Discover what you really are." Not too revealing, other than to suggest that there's more to what's going on than one might assume until starting to discover the story elements (intentionally somewhat left out of main areas of play).

Suggest alternative play styles. Although many people will have their preferred play style(s), providing achievements that emphasize a specific style is a good way to get players branching out, possibly discovering additional ways to enjoy the game, or simply approaching a new style as a different challenge. "Explosive Specialist" ("Destroy 100 hostiles with at least 90% of damage dealt by explosives.") is one of the more straightforward examples, likely requiring a dedicated build focused more around blowing things up for an extended period. And not just a build but the associated tactics and long-term strategy as well--specializing in explosive-based combat means paying extra attention to matter acquisition and consumption, managing the risks of likely opening up a lot of terrain and increasing exposure across the combat zone, and dealing with the likely higher alert that results.

Require a minimum difficulty level for certain achievements. This one's pretty unfair to some people who enjoy unlocking achievements, those who just want to play at their own level, undermining the purpose of adding difficulty levels in the first place.

Have separate achievements for every achievement at every difficulty level. Even though it's possible to automatically award same-type achievements of a lower difficulty each time a new one is earned on high difficulty (important to avoid forcing better players to also play at a lower difficulty just to earn achievements), I'd prefer to avoid massively bloating the achievements list like this. An informal poll of current players showed that most people were against achievements for different difficulty levels. Instead I'd like to just make it possible to clear achievements in case a player wants to permanently move up to a higher difficulty and start over. I did, however, make it so that the game internally records the highest difficulty on which each achievement was earned, so this data could be exposed in the future considering that Cogmind has its own achievement browsing interface.

Allow any achievement to be earned at any difficulty level. This is what I went with. Simple. Accommodating.

Mechanics: A group of mostly basic achievements covering common useful tactics and learning about systems. Even the obvious ones can serve as a way to reinforce features that players may accidentally trigger without realizing it. These make up over a quarter of the total, as there are quite a few different suitable mechanics.

Style: Specifically play style-related achievements, like combat, stealth, hacking, etc. These are generally earned through normal play using a given style/strategy, and while some might be more challenging or require focus in a certain area, they're not difficult enough to be considered "special challenges " (a separate category).

Progress: Personal meta progress like high scores, lore/gallery collection, and world exploration.

Challenges: This group doesn't have anything to do with Cogmind's "Challenge Modes," but are instead achievement-specific individual challenges ranging from Tier 1 (not too hard) to Tier 2 (hard) to Tier 3 (pretty hard!). This is currently the smallest category, but is also the most likely to grow if and when more achievements are added in the future. (It's also the smallest because a fair number of challenges are siphoned off by the later Wins category.)

Events: Story-related elements. Basically once you've visited every location and exhausted all the branching possibilities of the plot, you'll have all of these. This category is entirely hidden, though, so these aren't achievements to be explicitly sought out as if going down a list. You've just gotta explore and maybe in some cases use the in-game lore as clues to find more out-of-the-way areas.

Wins: There are many different ways to win the game, whether achieving one of the seven unique endings or simply winning by overcoming other challenging scenarios, so these get a whole category of their own. A lot of win-related achievements are technically considered Challenges, but since they require a win at the end they're all collected under this category rather than the other one above.