Possible assist trophies

King Bulbin would make a pretty nasty Assist Trophy (In a good way).
 
To attack other enemies for you and be almost invincible?
Did you read the first part?
It's kinda rare to have a Final Smash after an Assist Trophy anyways(unless you put only Assist Trophies and Smash Balls as items), but I think the second part is unnecessary. You should be invincible during a Final Smash anyways, no need to actually have the ability to take away an Assist Trophy before its period of time 'till disappearance.
 
How about Alucard from Castlevania if Simon Belmont gets in? He can attack enemies with his sword and transform into a bat to fly around the stage.
 
Boidoh said:
Rosalina' if not playable.

Of course Rosalina is not going to be playable, even though I'd really like her to be.

I always thought of her as an Assist Trophy that could summon a Star Bit storm. If a Star Bit hits you while falling, it can cause some knockback, while it doesn't cause damage (like the Bumper). But, if you touch a Star Bit AFTER it falls to the ground, it can heal you.
 
Maxwell from Scribblenauts (creates items that dont harm the person who used the trophy. however, items that help the users but dont hurt anybody like mushrooms only work on them. and poison mushrooms shrink everyone except the user)
 
Magnus from Kid Icarus: Uprising (Slice and dice enemies)
Prince Fluff from Kirby's Epic Yarn (Can whip enemies with his yarn)
Tails in the Tornado from Sonic the Hedgehog 2 (Flies around and shoots enemies and his plane can be used as a platform)
Kamek from Yoshi's Island (Flies around the stage and sprays magic which gives random status effects to all of the players)
Byrne from Spirit Tracks (Can shoot magical projectiles and shoot his mechanical arm)
Louie from Pikmin 2 (Summons the Titan Dweevil to attack enemies)
 
Blue-Bandanna Waddle Dee! He's playable in Return to Dreamland, so why not an Assist in SSB4? He could walk around the stage, jabbing people with his spear!
 
Raphael the Raven
When Raphael appears, he starts ramming through the stage. Getting hit by him doesn’t hurt you, but has BIG knockback.