Here is the full list of all 49 Never Give Up achievements.
Beat the final boss as blue (don't change costume).
Die 500 times in a single set
Beat final boss while wearing the Wizard outfit
Complete any level set in under 1 minute
Miss the cannon shot on the forest boss 4 times in a row
Reactivate a previous checkpoint
Complete 100% of the game
Complete 30 sets under their par times
Complete 16 sets under their par times
Complete 10 level sets without dying
Complete 70% of the game
Try on every outfit
Complete 30 level sets
Find your 30th collectable
Collect all 155 coins
Complete 8 sets under their par times
Complete 50% of the game
Defeat the final boss
Collect 120 coins
Complete 21 level sets
Collect the 3 golden keys
Complete 33% of the game
Activate 99 checkpoints
Complete 15 level sets
Find your 15th collectable
Have 20 missiles following you at one time
Collect 60 coins
Complete 20% of the game
Complete 10 level sets
Defeat the wizard boss
Resume a level
Complete 6 level sets
Find your 5th collectible
Collect 30 coins
Lose to the Warehouse boss by pressing the big red button
Complete 10% of the game
Defeat the first boss
Die near the exit point
Complete 3 level sets
Race and beat your ghost
Complete 2 sets under their par times
Complete 3% of the game
Complete a level set without dying
Die near the entrance point
Collect 15 coins
Find a collectible
Beat Laboratory
Collect 5 coins
Beat the game on Permadeath mode