Here is the full list of all 17 Impious Pumpkins achievements.
Kill 1 pumpkin of any kind.
Kill 10 pumpkins of any kind.
Kill ten thousand pumpkins of any kind.
Kill a thousand elite pumpkins.
Complete the Graveyard levels.
Complete the Haunted Mansion levels.
Complete the Alley levels.
Complete the Egyptian Tomb levels.
Complete the Corn Field levels.
Beat any level with an advantage of 50 ghosts.
Allocate every node in the melee branch of the skill tree.
Allocate every node in the slingshot branch of the skill tree.
Allocate every node in the mage branch of the skill tree.
Allocate every node in the healer branch of the skill tree.
Endure 5 minutes of pumpkin waves.
Endure 10 minutes of pumpkin waves.
Endure 15 minutes of pumpkin waves.