Welcome to the Family
Launching the game you literally can't miss this achievement. Maybe when you're opening the game in offline mode but I dunno.

Creators are here
In the main menu at the bottom left you should see this:

Click on it and it will show you the Credits (a little bit hidden, huh).

Customization
In the main menu click on the "ITEMS" section. No picture needed. I hope.

Let me show you how it's done!
For this achievement it should be enough to click on the "EDITOR" section. If not, then create a new map, pick a folder name for it and add an .ogg music file (you can get those through online converters) and press "CREATE!" (no icon needed). Publishing your map to workshop should not be necessary for the achievement.

Wait a minute... There are MORE MAPS???
This one got way easier by now. In the main menu click on the "SOLO GAME" section. At the top there are a few more sections that you can choose from. Go to "WORKSHOP" and simply download a map that interests you. Or just a random map. It's not really that important I guess.

Back in time
If it comes to dying after reaching a Checkpoint and then resume playing from it I can suggest "The Awakening", an official map, Star Wars themed. You only have to press 20 simple Arcs until reaching a Checkpoint. There you can die by pressing Esc or quickly tapping into wrong directions until your HP reach 0. In the end screen or rather death screen you then have the option to continue from "LAST CHECKPOINT". This should be all.

Still better than MOBA
You gain XP for your profile from completing published maps. This excludes editor maps. If you are playing through Official Maps (what's needed in later achievements) you should get this Level pretty fast. Combo is most important for your score, so try keeping that. :)
I'm not sure if Workshop maps still count, and if Funny and Loved maps ever counted. I'm Level 239 by now and don't get that much XP anymore. Hard to tell. ^^
As I said, stick to Official Maps, those will do the trick.

Collector
This achievement is a bit weird. I received it the first time I launched Intralism back in the day. There's a chance that the game automatically gives you an Item of each rarity at the beginning. If not, it helped for me to also own "Linea the game" another game created by KHB-Soft. Owning that game you receive special Arcs in Intralism, so maybe those caused that. If you don't get this achievement right away then I should talk a bit about the rarities.
There's "COMMON", "RARE" and "EPIC" items that you can receive and "LEGENDARY" items that are usually Event-Items, received through winning in contests or playing winner maps of those.
Common items you will have from the beginning, Rare ones have a blue outline in "ITEMS" section and Epic ones a yellow/golden outline. Through playing the game for an hour everyday (for me it's sometimes instantly) you receive an item every 24h. Getting an Epic rarity item is pretty... uh... not really happening. I had like 3 of them in my 830 play hours. Tho there is an option to craft items out of "Dust". There's Small, Medium and Large Cosmic Dust bags that you can get when turning items that you have into this Dust. As you can already imagine the rarity of an item decides if you will get a Small, Medium or Large Dust bag. Combining 6 small bags gives you a medium bag and combining 6 medium bags gives you a large one. 3 Cosmic Dust Large create an item with Epic rarity. Turning Rare items into Dust instead of Common ones will go way faster with that.
So if you have the patience you can wait for all those drops or invest like 10cents in Community Market to get one of those items.

Where are checkpoints?
I'm quite sure this achievement can be done alone in Multiplayer. Create a lobby and play through one of the maps you are subscribed to. Checkpoints are disabled in Multiplayer that's why the achievement is called like that. I'm not sure if the map you are playing will need to have a Checkpoint in it but I think No. If it does need one -> again "The Awakening" is a short and easy Official Map.

Hey! Look at THIS!
I'm not too sure if this Multiplayer achievement can be done alone. It simply says to play a workshop map that you've downloaded in Multiplayer. That doesn't really need another player to be around, the focus here is on the map being from Workshop. If this doesn't work alone, try to find a person you can play a map with that you like from the Workshop. That's basically the intention of the achievement.

Almost competitive
Once again it's too long ago for me to remember if this needed another player in your Lobby. If playing a map on your own in Multiplayer gave you this achievement then it's basically done. If not, find another player to play with and win against them (maybe ask them if you are allowed to win once for the achievement).

Party 2 everybody
This one definitely includes another player. Not sure if you have to play through an entire map or if it's enough to just have another person in your Lobby. Tho you can just play a map together if two of you already happened to go into a Lobby. Doesn't happen that often in the current state of the game. :P

Forever alone
If you go through this achievement guide chronologically you should already have this achievement by now. If... for some reason... you did all of the previous achievements with another player, just play a map without another player in Multiplayer now.

Arcade mode
At the time where I'm writing this guide there's only 11 Official Maps so you most likely have to go through some harder ones as well. Playing them in Normal mode instead of Relax means that you have limited HP so you need to perform somewhat good. Mistakes are of course allowed so its only important to reach the end of an Official Map. It is also said that it has to be 10 different maps, not the same one over and over again. Weird with this achievement was that I got it yesterday popping up in the bottom right of my screen. . . Without having launched the game in like a few days. :D
So yeah, that's for the Off-Topic. If there will be more easier Official Maps in the future this achievement will get easier. For now: Good look completing 10/11 of the Official Maps.

iddqd
This old cheat code is mentioned here in a secret achievement that wants you to complete a difficulty 4.5 or higher map from the Official Maps list with more than 90% (0.90) Accuracy. Currently there's only the Anubis map and Take A Hint. Since Take A Hint keeps the same pace of Arcs spawning for most of the time and since its shorter you definitely get this achievement the best way by playing that map. It's also fun so ~ Win/Win.

Self destruction
This one took me longest to figure out, but in the end I did find out on my own. \o/
I like this one. It want's you to create a Lobby in Multiplayer and then kick yourself from it by pressing the small X-Button in the top right of your Avatar.
The description of this achievement is pretty clear but since this is a secret achievement it only pops up when you got it and I only knew the name "Self Destruction" from looking at the global achievement statistics so at first I tried dying in different ways on different maps.
Was fun to figure out. Guess I just ruined the fun for every reader. Sorry.

And then you apparently hit the maximum characters of a section in the Steam Guide Creation thing...

First steps
Receiving your rank means playing an Official Maps since their scores add up on a global leaderboard. As long as you didn't play an Official Map your rank will be #TBD (to be destined).

I hate trends
This achievement requires you to go into "SOLO GAME" again and then in the "WORKSHOP" section. Here you click on the button "SORT" in the bottom left and then a window pops up where you can switch from "IN TREND" to "RECENT" or "TOP RATED".
I put it to Recent and pressed "APPLY" and that gave me the achievement.

No stress
You can take the achievement name literal. Pick any 5 maps you want (Official or Workshop) and simply start them in Relax mode. And you don't even have to play them. You don't fail in Relax mode so just pick 5 short ones and then wait for them to be over.
eZ

Misslick
This achievement will be automatically obtained when you do what I just told you. You can still do missclicks in Relax mode if you press into a direction where no Arc is. But if you press nothing at all, passing by Arcs won't count as mistakes so you end up with 0 mistakes and receive that achievement as well.
Weird but...
eZ

The judge
Rating a map is simple. After you finished playing there will be a thumbs up and thumbs down display on the map icon. Just decide to give the map a like or a dislike based on how you enjoyed it. This can be done without playing the map at all after downloading it. There you can already rate it as well by hovering over the map and then clicking on the Thumbs Up symbol.


And I think that's it.
If there were mistakes in sentence building and words (of course there were) then that's because it's not my native language. I'm sure tho that everything is understandable.
If any of those achievements won't work for you please tell me about it in the comments section below.
Thank you for your attention. :)
Have fun in Intralism