Here is the full list of all 43 Mr. Bree+ achievements.
Enter the first slaughterhouse level
Beat 20 levels
Die 100 Times
Die on the first level
Beat the tenth level
Die 50 Times
Get Run
Collect 5 bad memories
Die 10 times in the same level
Beat 5 levels
Quit a level
Get Crouch
Stay still for a while
Die 5 times in the same level
Collect the first bad memory
Die 1 time
Get Jump
Get Wall Jump
Get Double Jump
Collect 20 bad memories
Collect all bad memories
Beat 40 levels
Defeat the forest boss
Defeat the slaughterhouse boss
Beat 5 levels without dying
Beat 20 levels without dying
Beat 40 levels without dying
Beat all levels without dying
Beat your best time 10 times
Beat your best time 20 times
Press the red button!
Perform your first double jump
Get 50% of all achievements
Get 75% of all achievements
Get all other achievements
Skip the last cutscene
Watch the credits cutscene to the end
Start a level in hardcore mode
Beat 5 levels in hardcore mode
Beat 20 levels in hardcore mode
Beat 40 levels in hardcore mode
Beat level 24 in less than 29 seconds
Complete all levels in all game modes