Some Steam games don't have their achievements pop up until you close them. This is was one of them when it was released, but this has since been changed in a patch.

Also, if one player gets an achievement in co-op, everyone does.

And Gotta Get 'Em All is currently buggy and unobtainable. This used to also be true for Found All The Backers! and The Worst Possible Luck, but those have since been fixed.

A Timely Splash
Save yourself from burning up by jumping in water


Backer Visitor
Visit a backer character
- Easy enough; they generally appear on small islands just off the edge of the main bit of land on the level.


Boom Box Baby
Use The Boom Box 4 times in one game


Boom Box Wipeout
Pop 8 or more Earthlings who are dancing at a boombox


Can't Touch This
Beat normal or hard mode without dying


Cleaning Out Santa's Sack
Catch Santa 3 times in one game


Elf Chaser
Catch 5 elves in one game


Flying Present Catcher
Collect a locked present


Food Taster
Eat every type of food in one game


Fool Me Twice
Go for a ride in the Evil Elevator twice in one game


Found All The Backers!
Visit all backer characters


Gimme My Presents Back!
Pop a mole who has stolen one or more of your presents


Harsh Love
Make other player snap out of being in love by slapping them


Hey, You Did It!
Complete hard mode


Hi Fiver
Hi-Five another player 3 times in one game


I'm A Total Saint
Use Heal Friend Present on another player 10 times in one game


Is This Really Possible?
Beat normal or hard world without opening a single present


Mad Hatter
Unlock all power hats


Made It Through
Complete a random world game


Map Explorer
Uncover all the map tiles for 3 levels within one game


Nine Funkotronians
Play as each of the playable characters


Old School Jammin'
Play as both old Skool TJ and as Old Skool Earl in a single game (co-op)


Pacifist Victory
Beat normal or hard mode without popping a single Earthling


Piece O' Cake
Complete a fixed world game


Rhythm Star
Beat the 5th level in Rhythm Matching


Ridiculously Generous
Give a life to another player 3 times in one game


Struck By Love
Get hit by Cupid's arrow 5 times in one game


Sunflower Master
Hide in sunflowers 4 times in a game when being chased by an Earthling


Teamwork Rules
Complete a game with a friend (local or online)


The Worst Possible Luck
Open an unidentified Major Randomizer, Total Bummer, or Instant Demotion after level 20


Thrill Seeker
Open unidentified presents 15 times in one game


Truly Evil
Send an identified bad present to another player


Wakey Wakey
Make other player wake up by shouting at them


Why Do I Keep Doing That?
Have 10 broken presents blow up on you

99 Problems (But A Buck Ain't One)
Have 99 bucks


Achievement Achiever
Description to be added


Beaten By A Little Girl
Get killed by a Little Girl with a Teddy


Fall Fest
Fall off levels 5 times in one game


Feet On Funkotron
Get to secret Funkotron Level via a secret doorway


Flying Present Ultimate Catcher
Collect all of the locked presents


FunkLord Power
Reach the rank of FunkLord


Gotta Get 'Em All
Pop at least one of every bad Earthling type in one game


Hate That Randomizer
Open the Major Randomizer or Baby Randomizer 3 times in one game


HFZ Goober
Hit and leave through the very first exit in the HyperFunk Zone


I Can't Believe I've Done This
Get a game over before level 3


Level Diver
Get to hot tub island
- Use an item which allows you to teleport or travel across/above water, such as an Innertube or Icarus Wings, and head directly south of the starting island on level 1 to find another island with a hole in it. Fall through the hole to reach level 0 and get this achievement.

Lord Of The HFZ
Reach the end of the HyperFunk Zone


Totally Bummed Again
Open the Total Bummer twice in one game