Snail Bucket was added in Beta 50.0. Previous Versions can be found here.
As the name implies, Snail Bucket works with Snails, but it not one itself (much like Snailmobile and Snail Trainer).
Snail Bucket is the only Snail-related card to have a Dust effect, which makes it summon a Red Snail and a Yellow Snail, followed with one of them having their Magic effect triggered.
Because the Snails are summoned right away, they will trigger Snail Pen's effect as well, making one Snail Bucket trigger 3 Magic effects.