Assist Trophy: Waluigi

 I just don't think Waluigi should be a character until he has his own game, which isn't a bad idea. Waluigi's clearly a pretty popular character, and Nintendo is low on fresh franchises. Once he starts in a game or at least gets some possible moves, I'm all for Waluigi to be a character. Until that day, an assist trophy he should remain.

Stage: The Impact Site

I personally thought that the "Distant Planet" was a really stupid concept for a Pikmin stage. Why couldn't they have named it after one of the stages? I think that the Impact Site could be a very similar stage to the distant planet, with a few exceptions. One thing that could change would be that there would be something instead of a bulborb at the right. Maybe a wall that could be broken with enough damage or another piece of scenery. The ship in the background would still remain there.

Trophy: Joshua

Giving Joshua a spot as a trophy would be okay in my books. He's not really that important to the franchise, but he's really cool. Maybe one day he could become an assist trophy.

Item: Cucco

The most iconic animal in the Zelda universe, cuccos are annoying and useful and the same time. You could use a cucco to float for a long period of time. But the downside to these birds would attack you in large numbers (just like in the games) if you hit them with enough damage.

Item: Teddy Bear

The teddy bear was an item in Earthbound you could buy. It would follow you around and take certain damage for you from enemies for around 200 health points. I think it would be an awesome addition as an item, because it's a unique concept.

Assist Trophy: Ivan

 

Ivan should be the final of the three assist trophies to appear in Smash Bros. 4. He could use his Earth PSI or his staff to attack enemies.

Trophy and Sticker: Balloon Fight Enemy

The only enemy in Balloon Fight that you can defeat. It is important enough in my opinion to be both a trophy and a sticker.

Sticker: Marcus McCloud

The son of the greatest mammal in all of Corneria, Marcus has never been seen in action, but should get a little bit of recognition. I'd say a sticker would do the trick.

Bosses: Wart

The boss of Super Mari Bros. 2, Wart deserves an appearance, especially since he hasn't even appeared as a trophy yet or even just a sticker. I don't think he should ever be a character, but should consistently be a boss for you to fight. He could spit out bubbles and jump up and down similar to the way he attacks in Super Mario Bros. 2.

Starfy Enemies

 Pearl Sprites seem fairly common throughout the series

 

Jellysquishes seem to be a perfect wimpy and common enemy, but still essential

 Octopults I guess are somewhat similar to Octoroks from Zelda

Taddledogs just flat out look really cool and I want to see them in action

As I said, I don't know too much about this series, but I looked around and these enemies look like the most ideal enemies to use.

Peach

First Appearance
Donkey Kong
Arcade
1981

The most annoying character in the Super Mario Bros. series. Needs rescuing in nearly every game, from her first appearance as "Paula" aka Mario's girlfriend. She still is important, though. She has recently appeared in her own game (Super Princess Peach), has been in many mario spinoff games, and an become an iconic Nintendo character who can finally hold her own weight instead of riding on the Mario Bros.

The only move change I think she should have is making her standard special move use Toadsworth instead of just Toad.