World 6-3 (Super Mario Bros. 2)
There is a shortcut at the very beginning of the level that will take the player directly to Red Birdo. There is a wall to the left of the top of the ladder with quicksand underneath it. The player can use the quicksand to pass under the wall to reach a door on the other side, but must press the Jump Button(s) repeatedly to avoid losing a life.
The enemies of World 6-3 include Tweeters, Bob-Ombs, Ninjis, and a few Hoopsters; the environment is cave, desert, and sky. Before battling the boss of World 6, the player must defeat Red Birdo with a Mushroom Block and eggs. After Birdo is defeated, the player will enter the second fight with Tryclyde (Mouser in Super Mario Advance). This level is notable in that no key is found in the fortress.