The Nightmare Feather, or Flan-Bird, is an optional boss in Mario And Luigi: Pirate Galaxies. He appears in Mushroom Kingdom, freed from an alien egg. He is one of they only two bosses in The Mushroom Kingdom, the other being Bowser for the tutorial.
After our heroes find a secret tunnel below The Fungi Fountain, they enter a dungeon-like room. Suddenly, the door closes, and a giant egg appears.
Suddenly, the egg hatches, and out pops Flan-Bird. The battle then begins, a team against a GIANT MUTANT BIRD!!!