Here is the full list of all 69 Squirm achievements.
The base game contains 66 achievements, and there is 1 DLC pack containing 3 achievements.
Get the GUN!
Get the DOUBLE JUMP!
Kill Dr. Ludo.
Kill Skelord.
Kill King Fatty.
Kill Blocka.
Remember me?
Reach the top of the green tower and get the key!
Are you sure you know how to pilot this thing?
Open the box...
Enter the inverse world.
Defeat Float.
That can't be all, could it?
Start looking for your purpose.
Beat the game.
He was past his expiration date anyway...
...fond of drink and industry.
Oopsie!
Ruler of his people!
That's messed up...
!!!
The best jokes are inside jokes!
See something you weren't meant to see.
Explode...
Fart 100 times.
Create a black hole by shooting a sun.
Get all 100 coins in the green tower.
Die 100 times.
Get the star in "The Workplace".
Get the star in "The Spookileum".
Get the star in "The Azurine Glacier".
Get the star in "The Blistering Castle".
Get the star in "The Green Tower".
Get a star in space... where they belong.
Collect half of the stars.
Collect all 6 stars!
Burn to death.
Die to spikes.
Fall into the shadows...
Enter the surprise party world!
Complete the surprise party world!
Beat the game in under 2 hours.
...eeeeeeeeeeee
Beat the game in under 1 hour and 40 minutes.
Beat the game in under 1 hour and 20 minutes.
Beat the game in under 1 hour.
Beat the game in under 1 hour. Including Purpose!
Beat the game in under 45 minutes. Including Purpose!
Get 0 coins in the green tower.
...
Enter "The Mirror Tower".
Take a look. It's in a book!
Beat zone 1 as Squim.
Beat zone 2 as Squim.
Beat zone 3 as Squim.
Beat zone 4 as Squim.
Rescue Crackers!
Click the 100% button on the main menu.
Defeat the Rainbow Sun and enter "The Rainbow Nexus' Core".
Three years later... one last challenge awaits: The Rainbow Nexus!
I guess he couldn't make up his mind...