Before even starting the game, you can go to the workshop and find many custom skins and mods to download and use in your game. Simply download both a skin and mod, and start the game. You don't even need to use them (or at least, I didn't). Simply downloading them should be enough. Make sure the tags specifically read Mod or Skin, otherwise you may find the achievement wont open.

Much easier than you'd think. It simply involves adding something to the workshop. Without the know how, this is tedious and extremely annoying as there are little to no guides, however, it's as simple as renaming 2 files and then selecting an in game option.
Firstly, find your Audiosurf 2 folder in your steam folders.
Most people's pathway consists of their Data (D:), Programs Files (x86), Steam, Steamapps, Common, Audiosurf 2.
Go into the mods folder, and copy + paste any of the modes you see. I did Mono, but you can do any. Rename the copied folder to anything you like, personally, I called mine Mecha Hitler, but you may choose to be more mature.
Go into your new folder, and there will be 1 file (normally the first) with .lua at the end. Rename this file with the name you put on the folder.

Now open the game, and go to modes, and you should see your mode on the bottom row in the mods section. Hover over the thumbnail, and you'll see an arrow in the top left, which will allow you to upload it to the steam workshop. After doing so, the achievement will unlock, following which, you should delete the mod, as it is work of the game's creator and not you.

This will come without trying. I got this entirely by accident. Simply fill your grid as much as possible, and you should unlock it when the combo is activated. If you're having trouble, try to get a large amount of blocks before a corkscrew, and grab the multiplier, which will easily net this one for you.

Super easy achievement. Simply finish any song and then recommend the song to friends using the button in the picture below. If you can't see the picture, there are three tabs with Retry, OK, and Recommend this song to friends. Simply press the recommend button.

With the amount of time required a lot of people have trouble with this one, however it's extremely easy if you know the right song. While I'm not a brony, I am aware of one of the more challenging songs you could play on the original Audiosurf called "Here comes Tom", by Art Attack. The song is mostly dubstep, and has 2 insane drops which will net you well over 11 seconds of air if timed effectively. Another song which is good for this if you don't wish to indulge in anything mlp related, is "Gimme That!" By Alex S. The best place to find these songs is youtube since most mp3's on other websites are remixes or edited.

Play a slow and easy 3 minute song on Ninja mode, and don't hit any of the obstacles. Really simple if you can find a good song, but can be difficult.

There's no easy way to beat this one. It's literally always difficult, regardless of the intensity of a song. The slower the song however, the better your chances are. I was able to achieve this by looking up slow 3 minute songs on youtube and downloading some piano yoga music. Just keep trying, and try to keep calm because it will most likely take multiple attempts.

This one is a little tricky. It requires you to catch 7 seconds of air with a 2.75x trick multiplier. This can be difficult, but I've found a song with the perfect section right near the beginning of a song I love very much. In the song search, look up "Phantom of the Opera", and the first one should be a cover by Lindsey Stirling.

You'll find just before one of the first drops, there is a pickup right before a zap obstacle. This is where you need to start.

Collect as many pickups as you can until each row is full, and then carefully avoid the rest. You need to do this in a very short few seconds, and then you will hit a wave, which if timed properly, will net you the achievement if you've met the outlined parameters. It can take a few tries, but that's the beauty of this song since it is right near the beginning. If you can't get it on the first smaller jump, try the next insanely large wave a few seconds ahead, although this may be harder to get to with a full chart. If you feel you will overfill, grab a zapper to knock out a pickup, and quickly grab another one.

I got this one whilst going for Puzzle Master.
Using pointman, pick up a paint colour (preferably red or yellow) and then approach a multiplier pickup (preferably 3x or 4x). When you find one, try to have a full chart, matching or not, and then before you hit the multiplier, drop the paint power up. This will get you a whole chart of one colour that will be multiplied by the powerup.

The requirement is to achieve a 150k score in puzzle mode with a single combo. So far the only known way to do this, is to collect a red paint power up, achieve and sustain a 4x chain multiplier, and then the hard part is locating a 4x multiplier with a full chart while still holding the paint and a 4x chain multiplier. With a full chart turned red, a 4x chain multiplier, and a 4x multiplier, you should be able to achieve the needed score. While very few people have this achievement, a few good methods have been revealed around. The song "Possess your Heart" by "Death Cab For Cutie" is one possible song, although long, has proven to be relatively easy in this video.
Credit for the video goes to Luzzifus (https://www.youtube.com/channel/UC8ltOXe55z_L5pHQx6H8VfA)

If you prefer a shorter but harder song, "I'm made of wax Larry, what are you made of?" by "A day to Remember" has a red paint power up very early on, and a 4x power up after the songs breakdown, which would leave most of the song available for chain multiplier building, however I haven't managed to obtain and sustain a 4x chain multiplier before reaching this point. If I complete this task, I'll upload another video.

Basically, you need to play the game for a few minutes every day for 65 days. When you start the game, the Now Playing section where you pick your music will have a predetermined song, which is labelled the song of the day. Play this song once every day, and you will slowly build up the numbers. I am yet to earn this, but honestly, it is a very simple task in theory and practice if you have a few minutes during days.

Very simple concept, but will require a LONG grind. Look for long songs up to 10 minutes to net you around 1 000 000 points each time. Note that even with large point building songs, this will take lots of playing to achieve. I'm still only just approaching my first 100 million, so I can tell you this will likely take a few hundred hours of playing. Maybe less with the right songs though.
I'm updating this section with recommended point building songs, including any people wish to share in the comments. I'll list the name and band, and then the expected point grab for a competent player, and if known before hand, the rounded off play time.
I will also include songs shorter than 6 mins or less which offer around half a mil points, as these can often be played multiple times in a short period to achieve the same scores as longer songs.

"Through the Fire and the Flames" by Dragonforce - 1mil+ - 7:20mins
"Save me" by Avenged Sevenfold - 1.7mil+ - 11mins
"Red 13" by ParagonX9 - 1.05mil - 7mins (recommended by Gragon73)
"Lucid" by Lockyn - 725,000+ - 5+ minutes
"I Won't See You Tonight Part 1" by Avenged Sevenfold - 700-800,000 - 9mins
"I Won't See You Tonight Part 2" by Avenged Sevenfold - 500,000+ - 4:40mins
"Tales of the Destinies" by Babymetal - 5-600,000 - 5:30mins
"Ijime, Dame, Zettai" By babymetal - 6-700,000 - 6 mins
"Beelzeboss" by Tenacious D - 500,000 - 5:30mins
"Time is Black" and "Nemesis" by Arch Enemy - 450-500,000 - 5 mins
"Hardware Store" by Weird Al - 400,000+ - 3:50mins
"Give me Secret" by Stylips - 430,000+ - 3:30mins
"Zelda Meets Metal" by 331Erock - 400,000+ - 3:30mins
"Little Guitars" by Van Halen - 400,000 - 3:40mins
"Original Prankster" by The Offspring - 400,000+ - 3:40mins (quite a few offspring songs are around similar values)
"Gorgeous Nightmare" by Escape the Fate - 350-400,000 - 3mins
"ReadySet" by Parametic - Unknown range - N/A (will soon attempt for a basic stat count.

These are just the ones I've found within the last hour I played before typing this. Comment your high score songs and these details and I'll throw them onto the list.

I hope this guide helps, and I hope I achieve the elusive puzzle master so I can complete it soon! Have fun everyone.