Bugaboom is rather large, about 20 times as big as Mario is, as seen when they meet in the opening cut-scene. He differs very differently from his species. His design portrays him as a green stag beetle with longer legs and there are also wings on his back for flight. His belly has a slot that lets him drop bombs and is only used during his second and third phases. He is one of the largest bosses non-Bowser bosses.
Super Mario Galaxy
As Honey Queen suggests, Bugaboom and his minions invaded the Honeyhive Galaxy/Kingdom to cause trouble.
In Super Mario Galaxy, Bugaboom is fought on a planet with two moons that Mario starts on (He needs the Bee Mushroom to make his way to the planet itself.) several Banandelions (flowers that Mario can use to swing into the air) and a tree with honeycombs that Bee Mario can climb on in the middle to plan his attack. There is also a river of water which will deactivate Mario's Bee Suit if touched by him. Under the planet is a black hole which will suck Mario in if he falls off the planet, causing him to lose a life. When Mario lands on the planet using the Bee Mushroom, Bugaboom jumps from the trees and lands on the ground ready to attack. First you have to jump on his backside and Ground Pound him, then he will jump in the air and start flying around, forcing Mario to use either the Banandelions or the Bee Suit to hit it, and when Mario Ground Pounds him again the boss will turn red and start twisting around in the middle of his flight, so Mario will have to time his Ground Pounds to when the boss isn't sideways. The Bugaboom will also drop bombs in the middle of his flight Once Mario deals one more Ground Pound to the boss's backside, the Bugaboom will fall to the ground and explode, making a Power Star appear.
Super Mario Galaxy 2
In Super Mario Galaxy 2, the Bugaboom makes an appearance in the level Bugaboom's Back, reprising his boss role. It is a secret boss in Puzzle Plank Galaxy.
In order to defeat it, the player needs to use Cloud Mario and Ground Pound he three times like in Super Mario Galaxy. He will do the same attacks, but the Banandelions on his planet have been replaced with springboards and the honeycombs on the tree are no longer present. When you defeat him, the creature blows up for a second and last time and then a Power Star appears again.
Bugaboom's name is a pun on the words "Bug-a-boo", a term which refers to monsters (generally minor ones from children's books), and "boom", referencing the bombs he drops from his bottom after Mario enrages him into turning into his red form.
In Japan, Bugaboom does not seem to have an actual name, instead being referred to with a title, クワカブトキング (Mandibug King).