Super Mario RPG: Legend of the Seven Stars (known simply as Super Mario RPG in Japan) is a role playing video game designed by Squaresoft (currently Square Enix) and released for the Super Nintendo in 1996. It was the first Mario role-playing game, and worked out fairly well with an action-command battle system.
In this game: Birdo appeared as a boss. She was first seen as an egg named Shelly who was found in Nimbus Castle (while the stronghold was under the control of the usurper queen Valentina). The egg was cared for by Shy Away, who intended to use the newborn Birdo as a weapon. When Shy Away saw Mario, she quickly abandoned her post and fled, leaving Shelly exposed. Mario could then speak to the Birdo inside Shelly, who would request for Mario to play with her. If Mario complied, a battle between his party and Shelly would begin.
Although Shelly would never attack or perform any malicious moves toward Mario and friends, the group (through attacking) could gradually split the egg open to reveal Birdo. She would cheerfully introduce herself and start attacking. After suffering more attacks from Mario and company, Birdo would also raise her attacking methods, beginning to shoot out the explosive Eggberts rather than normal eggs.
Defending on a turn in which Birdo shot out Eggberts would actually fling the explosive eggs back into Birdo's nest, where they could then be attacked so that they would explode and deal massive damage to Birdo herself. Despite the pain and anger she showed ambiguous signs of going through, Birdo eventually gave up mid-battle (though she actually suffered normal defeat and Mario's party earned battle spoils such as Experience Points as normally) due to the fact that she found Mario and his friends too cute to destroy. After defeating her she gives the key to Mario, Birdo remains within shelly and Mario gets to the back door of Nimbus Castle.