Stage 1. Crucket
Crucket are naturally timid Pokemon. While they can do some damage with their claws, choosing to attack means letting go of their bucket and exposing their soft shell. Because of this they tend to avoid battles, and usually prefer to withdraw into their bucket and use their claws to nip anything that might try to peek in.
Stage 2. Buckster
As Crucket evolve into Buckster, they begin to come out of their shell, or bucket rather. Buckster are very headstrong, literally. Much more willing to battle, Buckster's claws have developed a locking mechanism, which allows them to grip foe's limbs in preparation to pull them in for a devastating headbutt.
Stage 3. Crustail
Somehow it's bucket got bigger, no one knows how, but it's been confirmed to be the same bucket. It now seems to be a part of the Pokemon's body. In addition to being a near impenetrable armor for Crustail's back (the only area it can't guard), the bucket stores up to 200 litres of water, which Crustail can launch at high pressure from it's right claw. Crustail actively enjoy battling and like to keep a tally of battles they've won on their bucket.