Kaboomba

The Kaboomba is a walking cannon enemy that first appears in Super Mario World 2: Yoshi's Island.

Super Mario World 2: Yoshi's Island
Kaboombas only appear in The Cave Of The Mystery Maze and Raphael The Raven's Castle. They attack by shooting heavy cannonballs that fall to the ground and explode after a few seconds. Yoshi can safely stand on them, and eating them does nothing. An egg or Ground Pound disposes of them.

Yoshi's Island: Super Mario Advance 3
Kaboombas retain their role in the Game Boy Advance port, Yoshi's Island: Super Mario Advance 3.

Yoshi's New Island
Kaboombas make a return appearance in Yoshi's New Island.

Super Princess Peach
Kaboombas also appear in Super Princess Peach, where they are named Cannons. The Calm Cannon, a sleeping variety, also appeared.

Other appearances
Kaboombas and an unused big variant were originally designed during the development of Super Mario World, where they would have shot Green Shells. They would have had white shoes, which also appear in early assets of Super Mario World 2: Yoshi's Island.

Super Mario World 2: Yoshi's Island

 * Official Nintendo Player's Guide: He strolls slowly, but unleashes a painful payload. It's pretty easy to avoid this cantering cannon.

Trivia

 * The Player's Guide description for the Kaboomba is erroneously accompanied by an image of one of the cannonballs instead of the enemy itself.
 * Despite the Kaboomba's name being similar to the Goomba, they have nothing in relation to them.