Here is the full list of all 31 Ultimate Chicken Horse achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Fall into the void 100 times
Unlock a character
Play 10 games
Play 10 games online
Die with the coin 10 times
Kill people with traps 100 times
Unlock an outfit
Unlock a level
Die on barbed wire 10 times
Glue four blocks together
Attach two blocks together with glue
Play 30 games
Play 100 games
Play 50 games online
Play online with a local friend
Place 200 traps
Place 1000 traps
Unlock all levels
Unlock all characters
Unlock all outfits
Kill someone with an arrow 100 times
Kill someone with a hockey puck shooter 100 times
Wall jump 1000 times
Get 10 post-mortem points
Teleport 50 times
Enter sudden death 20 times
Get 50 coins
Score 50 comeback points
Score 100 solo points
Die 50 times in a black hole
Win without any special points