The Rocketbarrel Boost (バレルジェット, Bareru Jetto Barrel Jet), labeled Rocketbarrel Blast in the Super Smash Bros. Brawl instruction booklet) is Diddy Kong's up special move. The height the Rocketbarrel Boost will cover depends on how much the player charges the jetpack. The player can change the angle that Diddy travels by tilting the control stick left or right while the move is being charged; charging the move longer allows a more significant angle shift. Diddy falls slightly slower as the move is charging.
Touching an opponent while ascending will cause minor damage. The initial burst when used in the air may serve as a meteor smash, spiking the foe while Diddy recovers to safe ground. If Diddy is attacked while using the move, the barrels will fly off and become randomly-moving, unshieldable projectiles, exploding on contact with the stage. If Diddy hits a ceiling while using the move, he takes about 5% damage.
 Description from the Instruction Booklet
Boost up with rocketbarrels. Press and hold the B Button before releasing to launch higher.
 Rocketbarrel Pack
The Rocketbarrel Pack is a jet pack that Diddy Kong uses for Rocketbarrel Barrage and Rocketbarrel Boost. It has a trophy in Brawl:
If Diddy Kong uses Rocketbarrel Boost while swimming. Diddy will sink down a bit and then float back up. Before he floats back up a small splash animation will be seen at the top of the water.