Super Smash Bros Brawl is absolutely full of assist trophies, but there are many characters that seem to have been completely missed out. I want you to say which ones you want to see in SSB4 and what they should do.

I for one would like to see Bullet Bill as an assist trophy. Several would fly across the screen doing a smash attack type effect on hit. (As in they dont just take damage but also go flying.)

tails the fox :
The way you described Bullet Bill seems like it would be to over powered to consider.
Not to mention it was in the story mode if you played it so it was in the game but not
as an assist trophy.

Now here is my suggestion to change your Bullet Bill idea.
It would chase the player similar to how the Bullet Bills in the bowser stages of super Mario Galaxy did
and the missile bills in the other games did.

This means it would just chase the closet player ( whom didn't use the trophy that is. )
This would avoid it doing huge damage and being an unavoidable attack.

You could also use some of the many variants of the Bullet Bill like the following :

Bombshell Bill : ( The stronger Golden Bullet Bill from paper Mario. )
This would do the same as the previous but would do much more damage.

Banzai Bill : ( The much bigger Bullet Bill )
It could fly across the screen in a straight line and do damage to whomever it passes.

King Bill : ( The really really big Bullet Bill that appeared in the New Super Mario series. )
It would do the same as the Banzai bill but it would fill the whole screen and damage everyone
including the assist trophy user.

Finally there could be a Bullet Bill Blaster that shot up to five different and random Bullet Bills
out to do multiple damage, it would also mean the pattern would be unavoidable as it would be
difficult to memorize it.
These could easily be changed to Torpedo Teds on stages with lots of water.

My next idea that comes from the Mario series would be a thwomp.
This would work similar to how the snorlax you can get whilst throwing a poke-ball does.
It would fall straight down the screen.

This could also use its variants such as the Thwimp ( The small Thwomp )
This would probably be easy to avoid. But if it does it it would do huge damage.
( Just to re-balance it. )

Grrrol :
This is the rolling thwomp subspecies. ( Similar to the Spiky Tromp from Paper Mario. )
This would simply roll across the screen.

The Super Thwomp : ( The one that can break through certain floors )
This would destroy the ground that it landed through and the floor wouldn't return for at least
30 seconds or so.

Next I think would the the angry sun.
As seen in multiple games. This would slowly do damage for up to 30 seconds to everyone that is on the top floor of the stage.

Bandits could be used as well ( The sub-species of the shy guy which has it's own sub-species )
I know they would be lame so I suggest using one of the sub-species for it like the Green one that
throws Yoshi eggs at enemies,
The other one that could be used is the baseball bat one ( Yellow sub-species. )
If anything or anyone is throw at it it will attack them by sending it flying towards another player.

Next is the para-bomb. ( Parachute Bomb-omb )
These would fall out of the sky and land in multiple places.
They would do the same amount of damage that the Bomb-omb Item does.

Next idea that comes from the Mario franchise would be the balloon boo.
This would come on from either end of the screen in an attempt to blow everyone off the screen.

The next boo based assist trophy could be the Circling Boo Buddies from Super Mario world and New super Mario bros. Wii.
They would circle around the edges of the stage stoping people getting knocked up whilst building
damage. Thus if timed right you could easily knock someone off the stage.

Next is the Amp ( Electric ball from Super Mario 64 )
A few would appear and hover around the stage doing damage upon contact.

Dolphin : ( Super Mario World )
These would jump up from the bottom of the stage and carry players upwards. then fall down again.

The Foo : ( New Super Mario Bros. Wii and Wii U. )
They would fill the stage with mist / clouds making it harder to see.

Fuzzy : ( Specifically the one from Super Mario World 2 : Yoshi's Island )
These would do the same as in that game making the screen look trippy and disorientating.

Amazing Flyin' Hammmer Bro. : ( Super Mario World )
This would do exactly as it did in Super Mario World, throwing hammers from it flying left to right platform.

Magikoopa :
This could fire different kinds of magics across the stage to try and inflict damage.

Piranha Plants :
They would come from only solid floor ( indicated by dust so it can be avoided. )


Those are just some ideas they could take out of the Super Mario Franchise

tails the fox : I personally Would Love to see Little mac as a new character. His Trophy assist is somewhat a waste on some parts. He just feels like he has so much potienal that he could be more then just a Assist trophy

SuperCrash64 : Well he did get that wii game... so hopefully Nintendo will show some love for the little boxer

He could be in Super Smash Bros 4 for all we know. I agree, he would fit in as a playable character quite well.