Here is the full list of all 23 Pepper Grinder achievements.
Collect all series 1 stickers
Earn a gold medal time attack record for every stage of World 1
Defeat the final boss
Collect all skull coins
Unlock all hidden stages
Defeat the 3rd boss
Defeat the 2nd boss
Carve a giant pumpkin
Fall into some soup
Defeat the 1st boss
Find a Mandragora and take its money
Unlock a hidden stage
Unlock the stickerbook
Complete stage 1-1
Collect all series 2 stickers
Collect all series 3 stickers
Collect all series 4 stickers
Collect all special series stickers
Complete 100% of the game
Unlock all stickerbook pages
Earn a gold medal time attack record for every stage of World 2
Earn a gold medal time attack record for every stage of World 3
Earn a gold medal time attack record for every stage of World 4