Like all other summon-able plants and zombies, it must be unlocked at the Sticker Shop. This is most commonly unlocked in the reinforcement pack. It has the most health of all non-shielded Browncoat Zombies.
Its attacks are Zombie Hurt and Hard Rock Toss. Each Zombie Hurt attack deals 15 damage. Each Hard Rock Toss attack deals 25 damage and is sometimes used when their target is far. Its appearance is of the Buckethead Zombie from Plants vs. Zombies.
The Buckethead's primary weapon is called Zombie Hurt, it is a short range attack that deals 15 damage at a slow pace, however, other variants of zombies will have slightly different melee attacks each with different names. Bucketheads will prefer to use their melee attacks, moving in closer to the target to attack them directly.
Abilities
Hard Rock Toss: A long ranged attack which deals 15 damage. Bucketheads will only use Hard Rock Toss when their target is first sighted a long distance away, before moving closer towards the target to attack using their short ranged primary attack.
Strategies
With
Use this sort of how you would use Browncoat Zombies. Use it simply as a distraction that has the benefit of much higher health. It may be considered strong, as there is almost no direct counter to it, aside from maybe Chompers.
In multiplayer, Chompers may not want to eat it though, because it's a summonable zombie and a potential waste of time and abilities. Be wary of Hot Rod Chomper and Count Chompula as they activate their abilities by eating it.
Against
These zombies, although tougher and potentially more annoying to deal with as most plant classes, should not usually be considered dangerous or a serious issue.
On most difficulties of Garden Ops and multiplayer, these can usually be dispatched by a clip's worth of ammunition, and these, like most Spawnable Zombies, can effectively be dealt with by moving backwards, away from them, and emptying shots from your primary weapon into them until they are vanquished.
Usually these zombies are not worth using abilities on, however, if the player has a very critical level of health and is being actively attacked by one or more of these zombies, powerful offensive abilities such as the Shuck Shot, Butter Barrage, Potato Mine, and especially the Chili Bean Bomb are useful, and abilities that can allow the player to escape by stunning or blocking zombies such as the Time Snare, Goatify, Tallnut Battlement, EMPeach, Husk Hop, Hyper, Citron Ball, and Arcane Enigma will also come in handy. A Chomper with one or more of its abilities recharged can almost always easily deal with Buckethead Zombies.
Gallery
Plants vs. Zombies Wiki has a gallery for Buckethead Zombie.
Also, the player almost never sees the pirate versions in the game aforementioned, only in a few of the Story Quest missions before and including the Captain Smasher boss fight.