Tail Bowser

A Tail Bowser is a fake Bowser powered by a Super Leaf. They first appear in Super Mario 3D Land.

Super Mario 3D Land
Tail Bowsers first appear in Super Mario 3D Land. They attack much like a fake Bowser from Super Mario Bros., breathing giant fireballs and jumping around the stage, though they do not throw hammers. Only two Tail Bowsers appear: one in and the other in, the latter of which also swings its spiky striped tail to attack and destroy columns. Additionally, they are immune to projectiles. In order to defeat a Tail Bowser, Mario or Luigi has to press a switch at the end of bridge to make it collapse and send the Tail Bowser into the lava. After falling into the lava, Tail Bowsers bounce upwards and show their true forms (a Goomba in World 1, and a Magikoopa in World 5) with a Super Leaf beside them.

Mario & Sonic at the Sochi 2014 Olympic Winter Games
A Tail Bowser appears as a boss in Mario & Sonic at the Sochi 2014 Olympic Winter Games, specifically in Mario's Figure Skating Spectacular. The appearances of the stage and its boss are based off Super Mario 3D Land. It chases the team across a giant collapsing bridge, spitting fireballs at them. The team must hit four buttons at the same time to cause the Tail Bowser to fall into lava, where it turns into a Goomba and a Super Leaf.

Mario & Luigi: Paper Jam
While a Tail Bowser never appears physically in Mario & Luigi: Paper Jam, one appears on a Battle Card, taking its design from Super Mario 3D Land.

Trivia

 * Tail Bowser's Super Mario 3D Land artwork is in almost the exact same pose as Dry Bowser's artwork for Mario & Sonic at the Olympic Winter Games and Mario Kart Wii.
 * Although a coincidence, King Koopa's appearance in The Adventures of Super Mario Bros. 3 episode "Super Koopa" gained the appearance of a Tail Bowser.