All achievements completed on my personal account in about 3 hours (it is possible to do so in much less time, like about 2 hours).

All of the following 8 achievements listed below are possible in just one map

• Enter the seed: -1830469710 and play it. At the very beginning, fly a bit lower till you see the gap shown in the screenshot below.
  
• It will take several tries, but successfully flying through the gap will earn you all three praises, thus automatically the Grizzly one.
  
• It also gives you well over 10,000 points, allowing you to get all the combo achievements in one go, including the Greedy one, where you simply have to crash after getting through the tunnel.
  
• In order to get the rest of the combo achievements, take a hard right immediately after passing through the tunnel. Do not fly up or down, you will see an exit in front of you very shortly.
  
• Remember, your wings don't actually collide with walls (unless you encounter the rare bug that causes this, although it seems to have been patched at the time of writing this).

(Click to get higher resolution)
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C to the OMBO!
Complete a 1,000 points combo.
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Pathfinder
Complete a 5,000 points combo.
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Cheater
Complete a 10,000 points combo.
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Gettin' Greedy...
Lose 10,000 points in a crash.
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• This corresponds to the score you get after one constant stream of points collected by flying close to walls or gaining one of the praises mentioned below.
  
• If you crash before the combo ends, it won't count and you will not get the achievement. You can recognize the end of a combo when you hear the sound of a typewriter.
  
• The last one is, of course, the exception, where you have to crash before you register the points from a 10,000-point combo.

Close Call!
Gain the "So Close!" praise. This is possible by flying extremely close to a surface without crashing. It is generally easier to do so by flying through a narrow vertical gap.


Not Bad...
Gain the "Awesome!" praise. This is possible by flying through a narrow 'tunnel'. There are many such 'tunnels' in various maps that look like a square tube. It doesn't have to be long.


Welcome to the Olymp!
Gain the "Godlike!" praise. This is a combination of the first two praises, where you have to fly through an extremely narrow tunnel with a gap as close to the width of your body.


Grizzly
Gain all three praises in a single run.

Spread your Wings
As the description says, start a run and end it by crashing somewhere. Simple enough.
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Creator
Go to Maps > Create Map and enter a random number. This option is useful for completing some of the harder achievements that get easier with certain maps (mentioned later).


Flying Monk
Go to Settings > Gameplay and tick the 'Zen Mode' option. This will remove the sound of accumulating points and stop displaying your score (but will still count in the background).


Psycho
Go to Settings > Gameplay and tick the options 'Invert Vertical Axis' and 'Invert Horizontal Axis'. It is not advisable to play with these options enabled unless you are a 'Psycho'.


The cake was a lie!
Travel through a portal. It looks like a bunch of pink pixels usually found near the bottom or edges of a map. Doing so will teleport you to a different map and grant 1000 points.


Blackout
Go as far down or as far wide into the edges of a map as you can, till the screen turns all white. Doing so will teleport you to a different map (no bonus points awarded).


Explorer
Explore 25 maps.
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Adventurer
Explore 50 maps.
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Call me Dora...
Explore 100 maps.
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From what I've noticed, going to the edges of a map takes you to more new maps than portals do. This may, of course, just be a coincidence based on my personal experience. However, it is best to get these three achievements naturally by just playing a lot instead of grinding them.


9 Lives
Crash 50 times.
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Just one more time...
Crash 150 times.
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Please stop it!
Crash 300 times.
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Once again, it is best to just get these achievements naturally through gameplay.


Beginner
Get 5,000 points in a single run.
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Rising Star
Get 10,000 points in a single run.
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Expert
Get 20,000 points in a single run.
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Get a Life...
Get 40,000 points in a single run.

• This corresponds to the score you are supposed to get in one run until you crash. It doesn't matter how long it takes to get there.
  
• It is best to take fewer and fewer risks, the higher the score you want to get. Also, it is highly advisable to take as many portals as you can, since they not only give you 1000 points but also 'reset' your position by teleporting you to a new map.
  
• The best trajectory is usually to circle the map in a kind of downward spiral, staying near the edges and eventually taking a portal or exiting out through the bottom.

• Have fun! Don't just grind the game to get achievements! It's a lot of fun, and a lot of the achievements are possible just through casual gameplay.
  
• Save your favourite maps and revisit them! As far as I can tell, there is no limit to the number of maps you can save, and some of them are truly unique and beautiful in design and colour.
  
• Turn on Zen Mode and listen to some music in the background! I personally recommend this chill lofi playlist.