The bucket is a metallic headwear worn by Buckethead Zombies to protect themselves from being damaged. It is the strongest type of headwear in the first main series game. Since it is metallic, it can be attracted by a Magnet-shroom.
The bucket is a very strong piece of headwear, so the player should choose high-damaging plants against it, such as Winter Melon or Citron. Take note that it is a metallic headwear, so using the Magnet-shroom or the Magnet Plant can be a good idea as they can steal it, making the Buckethead Zombies easier to defeat. Don't always rely on this though, as there may be too many Bucketheads for you to handle, making the zombies get to your Lawn Mowers, or worse, your brains.