Here is the full list of all 16 Attack of the Gigant Zombie vs Unity chan achievements.
Defeat the grassland boss
Defeat the forest boss
Defeat the desert boss
Defeat the destroyed city boss
Defeat the simple city boss
Collect 30 items
Collect 60 items
Collect 120 items
Collect all record players
Defeat the Valentine's Day boss
Defeat the Easter boss
Defeat the Halloween boss
Defeat the Christmas boss