Here is the full list of all 15 Deadly Harvest achievements.
Complete the Farm level
Complete the Village level
Be decapitated by the Horseman
Reunite the Horseman with his missing head
Decipher the mysterious page
Find the secret message in the red house
Dig up the severed head
Purchase 10 Class Upgrades
Purchase 20 Class Upgrades
Unlock all starting weapons
Earn 150 gold in a single run
Destroy 500 corn stalks in a single run
Get 4 Pumpkin Pie slices in a single run
Hit a single enemy with the following weapons: Bell, Torch, Pitchfork, Striped Feather
Dig up the wrong head