Character unlocks differs between the 3DS and Wii U versions. I'm posting a complete list for both versions below. Source
Ness
3DS: 10 Smash matches or beat Classic mode
Wii U: Unlocked by default
Falco
3DS: 20 Smash matches or beat Classic mode without using any continues
Wii U: 10 Smash matches or beat Classic mode
Wario
3DS: 30 Smash matches or complete 100 man smash
Wii U: 20 Smash matches or complete 100 man smash
Lucina
3DS: 40 Smash matches or beat classic mode as Marth without using any continues
Wii U: 30 Smash matches or beat Master Core (classic mode final boss at intensity 5.1 or greater) as Marth at 5.5 intensity
Dark Pit
3DS: 50 Smash matches or beat Classic mode with three or more characters
Wii U: 40 Smash matches or beat All-Star mode on Normal
Dr Mario
3DS: 60 Smash matches or beat Classic mode as mario at intensity 4.0 or greater
Wii U: 50 Smash matches or beat one Master Order on hard difficulty
R.O.B.
3DS: 70 Smash matches or collect 200 trophies then play a Smash match or beat classic mode
Wii U: 60 Smash matches or defeat Crazy Hand after completing 10 matches in Crazy Orders
Ganondorf
3DS: 80 Smash matches or beat Classic mode as Link at intensity 5.0 or higher
Wii U: Unlocked by default
Mr.Game & Watch
3DS: 90 Smash matches or beat Classic mode with ten fighters
Wii U: 80 Smash matches or beat Classic mode with five fighters
Bowser Jr
3DS: 100 Smash matches or beat Classic Mode as Bowser on Intensity 6.0 or higher
Wii U: Unlocked by default
Duck Hunt
3DS: 110 Smash matches or beat Classic Mode with 8 or more characters
Wii U: 100 Smash matches or KO one fighter in Cruel Smash
Jigglypuff
3DS: 120 Smash matches or collect 30 different equipment items
Wii U: Unlocked by default
DLC Characters
Mewtwo
3DS: $3.99
Wii U: $3.99
Both: $4.99
Lucas
3DS: $3.99
Wii U: $3.99
Both: $4.99
Roy
3DS: $3.99
Wii U: $3.99
Both: $4.99
Ryu W/ Suzaku Castle
3DS: $5.99
Wii U: $5.99
Both: $6.99
(Note: This DLC comes with the stage as well as the fighter)
Cloud W/ Midgar
3DS: $5.99
Wii U: $5.99
Both: $6.99
(Note: This DLC comes with the stage as well as the fighter)
Corrin
3DS: $4.99
Wii U: $4.99
Both: $5.99
Bayonetta W/ Umbra Clock Tower
3DS: $5.99
Wii U: $5.99
Both: $6.99
(Note: This DLC comes with the stage as well as the fighter)
This is not yet a complete list, and it's based on the European version of the game. The wording for the US version can be different.
Playing and Clearing
Smash
- Started playing Super Smash Bros. for Wii U!
- Battled 10 times now!
- Battled 50 times now!
- Battled 100 times now!
- Battled 200 times now!
- Encountered Mew for the first time! Strange things do happen.
Smash Tour
- Played Smash Tour for the first time!
- Played a total of 100 or more turns in Smash Tour!
Classic
- Cleared Classic for the first time!
- Cleared Classic with every fighter!
- Cleared Classic at intensity 9.0: Nothing Harder!
All-Star
- Cleared All-Star for the first time!
- Cleared All-Star on Hard!
- Cleared All-Star with every fighter!
Special Orders
- Cleared an Intense stage in Master Orders for the first time!
- Cleared Crazy Orders for the first time!
- Cleared Crazy Orders after getting through 10 rounds!
Events
- Cleared 30 challenges in Solo Events!
- Cleared all challenges in Solo Events!
- Met the reward requirements of all Solo Events challenges!
- Cleared 10 challenges in Group Events!
- Cleared all challenges in Group Events!
- Met the reward requirements for all Group Events challenges!
Stadium
- Won 100-Man Smash for the first time!
- Defeated 300 enemies total in Endless Smash!
- 5000 targets and obstacles blown up in Target Blast!
- Got over 400000 points in Target Blast!
- Cleared the 1000m mark in the Home-Run Contest!
Trophy Rush
- 1000 blocks blown up in Trophy Rush!
- 5000 blocks blown up in Trophy Rush!
- Obtained 500 trophies in Trophy Rush!
Online
- Got a Global Smash Power rating!
- Got a Global Smash Power of over 100000!
- Collected every online profile icon! Pick the one that's right for you!
Unlocking
Fighters
- Unlocked Falco!
- Unlocked Dr. Mario!
- Unlocked Wario!
- Unlocked Mr. Game & Watch!
- Unlocked Lucina!
- Unlocked Dark Pit!
- Unlocked R.O.B.!
- Unlocked Duck Hunt Duo!
- Unlocked all fighters! Now the real battle begins!
- Unlocked the true All-Star solo mode! Find it in Games & More.
- Mewtwo, the reawakened legend, has joined the battle!
Stages
- Unlocked the Kongo Jungle (64) stage! Master the mighty Barrel Cannon!
- Unlocked the Smashville stage! You might even get to see K.K. Slider performing live!
- Unlocked the Pokémon Stadium 2 stage! It's a roller coaster of different elements!
- Unlocked the PAC-LAND stage! Guide the fairy home, then go back home yourself!
- Unlocked the Duck Hunt stage! Get into the retro groove!
- Unlocked the Flat Zone X stage! Can you name all seven games?
- Unlocked all stages! Time to learn all 46 in and out!
- Unlocked the Random Stage Switch option! Find it by selecting Smash, then Rules.
Demos
- Unlocked a demo of the classic title Earthbound! Play it in Masterpieces!
- Unlocked a demo of the classic title Mario & Yoshi! Play it in Masterpieces!
- Unlocked a demo of the classic title Kirby's Adventure! Play it in Masterpieces!
- Unlocked a demo of the classic title Punch Out!!! Play it in Masterpieces!
- Unlocked a demo of the classic title Dr. Mario! Play it in Masterpieces!
- Unlocked all of the Masterpieces! Now you can really delve into the fighters' origins!
Collecting
Songs
- Collected over 350 songs!
- Collected over 400 songs!
- Collected every song - a smashing playlist!
Trophies
- Collected 100 different trophies!
- Collected 200 different trophies!
- Collected 300 different trophies!
- Collected 400 different trophies!
- Collected 500 different trophies!
- Collected 600 different trophies!
There's no milestone for 700 trophies, even though there are more than 700 to be found. There is one for all trophies, but I'm one short so I don't know the exact wording.
Moves
- Collected 50 types of custom special moves!
- Collected 100 types of custom special moves!
- Collected 200 types of custom special moves!
- Collected 300 types of custom special moves!
Equipment
- Found 30 unique bonus effects for equipment!
- Found 40 unique bonus effects for equipment!
- Found 50 unique bonus effects for equipment!
- Found 60 unique bonus effects for equipment!
- Found 70 unique bonus effects for equipment!
- Found 80 unique bonus effects for equipment!
- Found 90 unique bonus effects for equipment!
- Collected 100 pieces of custom equipment!
- Collected 200 pieces of custom equipment!
- Collected 300 pieces of custom equipment!
- Collected 400 pieces of custom equipment!
- Collected 500 pieces of custom equipment!
- Collected 600 pieces of custom equipment!
- Collected 700 pieces of custom equipment!
- Collected 800 pieces of custom equipment!
- Collected 900 pieces of custom equipment!
- Collected 1000 pieces of custom equipment!
- Collected 10 types of custom headgear!
- Collected 20 types of custom headgear!
- Collected 30 types of custom headgear!
- Collected 40 types of custom headgear!
- Collected 10 types of custom outfits!
- Collected every type of custom outfit! Your body is ready!
Best Answer
The Amiibo will not unlock that character. The Amiibo just becomes an AI controlled character, which can be placed on your team or play against you.
There is no difference between the different versions of the game.