Booom is an Instrumii that first joins your party in Chapter 1 of Paper Mario Instrumental. He was captured by Bowser so he couldn't assist Mario to get through his fortresss.
He uses sound waves to break things (like Bombette or Admiral Bobbery just he's not a bomb)
He looks like 2 floating speakers with eyes.
HP (when first met):10
-Sound Shoot (FP:0) (Damage:2)
-Body Slam (FP:2) (Damage:4) (May Paralyze)
-Sound Explosion (FP:5) (Damage:7) (Damages every enemy)
-Sound Barrier (FP:3) (Damage:0) (Protects any attack and attacks can be used for Mario and Co.)