A Goomba Tail
From the Super Mario Wiki
A Goomba Tail is the first secret level of Teehee Valley in the Minion Quest: The Search for Bowser mode in Mario & Luigi: Superstar Saga + Bowser's Minions. In order to obtain this level, the player has to use certain amiibo to unlock it.
The level consists of mostly Goombas, Paragoombas, and Big Tail Goombas and has only three battles. The first battle has four Goombas, one Big Tail Goomba, two Paragoombas, and a Big Tail Goomba captain. The second battle has two Big Tail Goombas, four Goombas, one Paragoomba, and a Paragoomba captain. The third and final battle has one Big Tail Goomba, two Goombas, four Paragoombas, and a Big Tail Goomba captain.