Advise from the Smash God himself.

Learning Classic Mode

https://www.youtube.com/watch?v=gYX4wWkX_Fo

Unlock All Characters Route

First things first, how to get a new save file.
What I did and seems to be the most reliable thing to do is copy your current smash save file to a USB Port.
Once you have a smash file on both your system memory and USB you can delete the save data from your system memory. This will keep the save data on your USB but still give you a new game on system memory. 
Turn off your WiiU once you Copy, and than delete your save memory off your system memory and remove your USB Port after the WiiU is turned off
Start up the game and now you can start the run!
Timer starts when you hit any button at the selection screen

Falco - Clear Classic
Wario - Clear 100 Man Smash
Lucina - Clear Classic on 5.5 or higher
Dark Pit - Clear All Star Normal
Dr. Mario - Clear Master Orders Hard
R.O.B. - 	Clear Crazy Orders after 10 rounds and defeat Crazy Hand
Mr. Game & Watch - Clear Classic Mode on intensity 2.0 or higher with 5 characters
Duck Hunt - Earn 1 KO in Cruel Smash

Listed above are all the characters you have to unlock and how to do so
I will put my current route that I think is the fastest and will edit if need be.

Classic 2.0 Ganondorf
Unlock Falco
Clear Classic 5.5 Bowser
Unlock Lucina
Classic 2.0 Rosalina & Luma
Classic 2.0 Ness
Classic 2.0 Captain Falcon
Unlock Mr. Game & Watch
All Star Normal
Unlock Dark Pit
Clear 100 Man Smash
Unlock Wario
1 KO in Cruel Smash
Unlock Duck Hunt
Master Orders on Hard
Unlock Dr. Mario
Crazy Orders (10)
Unlock R.O.B.

InprisonedShadow

RubberDuckyAssassin

yesman419

Super Smash Bros. for Wii U

Mario

Luigi

Donkey Kong

Greninja

Wii U

MRHerow

OGHappydude

thorne_1154

USA / NTSC

EUR / PAL

Peach

Bowser

Yoshi

Rosalina & Luma

Bowser Jr.

Wario

Diddy Kong

Mr. Game & Watch

Little Mac

Link

Zelda

Sheik

Ganondorf

Toon Link

Samus

Zero Suit Samus

Palutena

Marth

Robin

Duck Hunt

Kirby

King Dedede

Meta Knight

Falco

Pikachu

Charizard

Lucario

Jigglypuff

R.O.B.

Ness

Captain Falcon

Villager

Olimar

Wii Fit Trainer

Shulk

Dr. Mario

Dark Pit

Lucina

Pac-Man

Mega Man

Sonic

Mewtwo

Lucas

Corrin

Bayonetta

Cloud

Co-op

Solo

Mii Brawler

Mii Swordfighter

Mii Gunner

Solo Customs

Co-op Customs

Player 4 Character

All Star, Hard Subcategories

Classic, 5.0 Subcategories

All Star, Normal Subcategories

All Events Subcategories

Multiman Smash (10) Subcategories

Multiman Smash (100) Subcategories

Classic, 0.0 Subcategories

Classic 9.0 Subcategories

All Star Easy Subcategories

Player 3 Character

Ironman Subcategories

Solo/Co-op

Solo/Co-Op

Player Count

Customs

Intensity

Difficulty

10/100-Man Smash

Player 2 Character

Super Smash Bros.

True All-Star Mode with DLC

Surprises…

Smash ultimate

100-man Smash Rules

New Speedrun Idea

Minimizing Load Times

TheTrooble

Tech

TMPet

Arahpthos

KCCKirby

Frosted48

kaialb

abuela

underscore58

Name	Author
Advise from the Smash God himself.	InprisonedShadow 10 years ago
Learning Classic Mode	yesman419 6 years ago
Unlock All Characters Route	RubberDuckyAssassin 8 years ago