Well I'm starting off with my old Melee fave, Jigglypuff!
Back in Melee, Jigglypuff was one of the best characters around! With Brawl came in and nerfed Jigglypuff to the extent that Jigglypuff is no longer viable to play with and is more or less of a Joke Character back in Brawl.
In Smash 4 however, Jigglypuff got Buffed to the extent that its usable again!
I did some research and found a comparison from Brawl
http://www.ssbwiki.com/Jigglypuff_(SSB4)
Changes from Brawl
Jigglypuff has been buffed from Brawl, although not quite back to its strength from Melee.
Neutral attack and up tilt have been sped up.
Up tilt, forward tilt, down throw and up throw do 1% more damage.
Neutral air, back aerial, up smash and back throw deal 1% more damage and have more knockback.
Forward throw deals 1% more damage and has slightly shorter endlag.
Dash grab has less ending lag.
Rest is significantly stronger than in Brawl, though not quite back to its Melee power. Due to the changes in hitstun mechanics, Jigglypuff can now perform true combos into Rest, greatly improving its utility once again. Rest also deals more damage.
Dash attack has less ending lag and is stronger.
Up air has more reach.
Back aerial is drastically more powerful to the point where it can reliably KO under 120%.
Because of this, it loses some of its Wall of pain ability.
Pound deals more shield damage.
Forward air does less damage.
Rollout deals much less damage and knockback.
Now uses its other arm to Pummel, instead of its hair curl.
These are based on the experience I had with the character
Rated upon 1V1 battles
Pros
-Has been buffed to the extent that is usable again
-Can reliably KO under 120%
-A lot of attacks has more knockback
-Good Aerial
-Amazing Aerial Recovery
-Got a bit faster
-Pound reduces opponent's Shield to upto 50%, so expect to break shields
-Can avoid Weapon-Based characters easily with Air dodge and can handle brawl-Type characters fairly well with Bair,Nair.
-Can easily Juggle
Cons
-Most Special Attacks got nerfed
-Expect to get launched high with low percentage
-Frail
-Shield Break = KO
-Hard to Maneuver for beginners
-Expect Swords to be your worst enemy(Mid-ranged characters)
-An Advanced Character