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.

Pikmin Enemies

 Yellow Wollywogs could jump up like they do in the Pikmin series, then slam anything below it

 Firey Blowhogs could spit fire at you

 Puffy Blowhogs could not do damage, but could push you or blow you from advancing

 

Bulborbs could be common enemies that bite you  rather than eat you

 Goolixes could move around, but you'd have to hit it's weak spot. If you hit its other spot, it would send you flying

 Mamutas could slam you into the ground

 

Armored Beetles could be a mini-boss or at least a very tough enemy

 

Pearly Clamp Clamps could hold items like a pokeball or a sticker, but could swallow you for a whole bunch of damage

 

Swooping Snitchbugs could grab you and throw you to the ground

Captain Olimar

 First Appearance

Pikmin

Gamecube

2001

The Captain will be another obvious choice. Only problem for him is whether or not his own series will continue. Nintendo has been very reluctant over the past decade to release anything out of their "circle" of games, which would be Zelda, Mario, Kirby, Pokemon, and Metroid. This mentality is stopping a lot of great series in its tracks like F-Zero, Earthbound, Donkey Kong, Starfox, and of course Pikmin. Nintendo has been saying every year since 2008 that they would release a new Pikmin, but they have yet to do so. Unless this game is a perfect game, there will be a lot of upset fans, more than there already are.

I would like to somehow see mushroom pikmin and bulbmin to somehow appear in Olimar's arsenal. Other than that, unless there's new Pikmin species in the upcoming Pikmin game, I think there's no need to change Olimar's moveset in any way.