From the Super Mario Wiki
Blast-O-Cannons are cannons that Wario can jump into and blast out of in Wario Land: Shake It!. Like pipes, Wario struggles for a short while to squeeze inside. The player can tilt the to blast out of the cannon and break through blocks that would otherwise have been unbreakable before, and also reach places inaccessible before and get to new ledges. In order to fire it, the player must hold the button to charge up and release it to fire the cannon. Moreover, Wario can blast into another Blast-O-Cannon. Doing this tends to be tricky, as these cannons tend to move to make things harder for him.
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