Here is the full list of all 26 Pixel Gear achievements.
Kill 60 or more Ghosts in a level
Perform 30 Combos during one play
Achieve the SSS Grade for the first time
Achieve the SS Grade or better for the first time
Achieve the S Grade or better for the first time
Achieve the A Grade or better for the first time
Achieve the B Grade or better for the first time
Achieve the C Grade or better for the first time
Use the Bat's Pumpkin to blast 4 or more enemies!
Complete the first stage without receiving any damage
Complete the second stage without receiving any damage
Complete the third stage without receiving any damage
Perform a total of 100 headshots to the Frankstein Monster
Perform a total of 100 headshots to the Knight
Perform a total of 100 headshots to the Skeleton Warrior
Perform a total of 100 headshots to the Witch
Deflect in total 30 enemy bullets in a row during one play
Kill 1000 Ghosts in total in the game
Kill 500 Ghosts in total in the game
Kill 100 Ghosts in total in the game
Use the Powder Keg to blast away 3 or more enemies
Perform 100 Headshots in total in the game
Use the “HP-Ghost" while having only 1 Life left
Kill 200 enemies with a Submachine Gun in total
Hurt 10 or more Angels during one play
Collect 200 Gold in total in the game