Assist Trophy: Birdo

Birdo is certainly an important character in the Mario series. She was the primary boss in Super Mario Bros. 2, along with appearing in dozens of Super Mario Party, Mario Sports, and Mario Kart games. I would say that she's more deserving than Waluigi for becoming a character, but she's another character that still isn't quite there. Maybe if they remake Super Mario Bros. 2 or if she gets a starring role in an upcoming Mario game, then she would be far more deserving of a slot.

For her move as an assist trophy, I think she could shoot eggs like she did in Super Mario Bros. 2.

Item: Mushrooms

 We all know the two types mushrooms in Super Mario Bros. However, in the Galaxy series along with the New Super Mario Bros., there were many new types of mushrooms. I think we should see a few of these in the next Smash Bros. The mega mushroom could make you as big as possible for a little while, but is much rarer than other mushrooms. The bee mushroom could give you the ability to fly briefly without any limitations. Lastly, the stone mushroom could make you unable to be knocked back, but in exchange you'd be slightly slower.