Thwackey is a bipedal humanoid monkey with a light-green colored body, and a lighter green for its face mask and chest marking. Its ears, arms, and tail are dark brown, and its two large eyes are yellow in color. It has dark green bands around its wrists, and a stick holding up a tuft of leaves resembling hair on its head. When it removes the sticks, the leaves resemble a fan, with dark green on the ends. It has several sharp teeth.
Thwackey can use its two sticks to create a rhythmic beat. The faster a rhythm Thwackey creates, the more respect it earns from its peers. Often, when it drums out rapid beats in battle, Thwackey will get so caught up in the rhythm that it does not realize its opponent has been knocked out. To further develop its sense of rhythm, it constantly uses it in daily life. It can always feel a beat, and it walks while swaying back and forth to this beat, along with drumming with its sticks.