Here is the full list of all 23 Pepper Grinder achievements.
Unlock all stickerbook pages
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 1 stickers
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
Earn a gold medal time attack record for every stage of World 1
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