Goomba Tower

Goomba Towers are Goombas stacked on top of each other (ranging anywhere from stacks of 2 to stacks of 10) that first appeared in Super Mario 3D Land.

Super Mario 3D Land
Goomba Towers attack by running at the player and attempting to hit him or her in a similar fashion to individual Goombas. Goomba Towers can be shortened or defeated depending on how many Goombas the stack has. For example, attacking jumping on a stack of 4 will reduce it to a stack of 3, and so on. Alternatively, they can be killed all at once with a Ground Pound or as Statue Mario in statue form. They can be defeated one-at-a-time by being jumped on, being hit with a fireball, or whacking them with Tanooki or Statue Mario's tail.

Two Goomba Towers are seen in Peach's Letter when they try to attack Princess Peach. Peach manages to hit the Goomba Tower using her parasol. A Goomba Tower is seen chasing Peach with Bowser and his other minions. During the credits, Bowser is seen climbing up a massive Goomba Tower, trying to reach Mario, who is carrying Peach home in his Tanooki form, but this ultimately fails.

New Super Mario Bros. 2
Goomba Towers reappear in New Super Mario Bros. 2, where they appeared to be stacked up even higher than before. The Goomba Towers can be defeated by the same methods as before. They can be affected by the Gold Ring, where they function the same as Gold Goombas, thus becoming a couple of Gold Goombas stacked together.

They first appear in World 1-1, where one three-stacked Goomba Tower appears before the Checkpoint Flag and one 8-stacked tower appears right before the Flagpole.

Mario Party 9
Goomba Towers appear in Mario Party 9 in the Goomba Spotting minigame, where players attempt to count the total number of Goombas that run across the screen as accurately as possible. Sometimes, Buzzy Beetles appear at the tower to trick the players into tallying them.

Paper Mario: Sticker Star
In Paper Mario: Sticker Star, five Goombas appear in a meadow-like area and stack together as a Goomba Tower to bend into a wheel as part of their dramatic entrance to attack Mario and Kersti.

Trivia

 * In New Super Mario Bros. 2, if Mario/Luigi defeat a number of Goombas in the Goomba Tower and leaves the remaining Goomba(s) so they're offscreen, upon returning, the Goomba Tower will be renewed with its original number of Goombas. Because of this, they're effective enemies to farm Coins from if under the effect of the Gold Flower, especially for Coin Rush mode.