**+1**
Ridley
Iconic, can be cloned off Charizard who has a similar body shape and a somewhat similar idea of fighting style : launch em up, combo em hard. I suppose Ridley would be more projectile and range-based (that tail in super metroid is so damn long) tho as opposed to Char's into-your-face style. Ridley should also diffirentiate himself from Char ; for example, Char is great at killing off the top and has phenomenal edgegame, so Ridley should be better at killing off the sides and at wall-of-paining.
Moveset ideas :
-Tail swipe (Downsmash ?) as seen in Metroid Prime where he turns around and deals heavy damage all around him due to his tail
-Charge (side-B ?) from Metroid Prime. Goes further when used from the ground.
-Fireball (neutral B ?) as seen on Meta Ridley in Brawl where he approaches the middle of the Falcon Flyer and shoots a bigass fireball that blows up half the stage. Chargeable from small harass to huge nuke. Shoots diagonaly down when airborne or forward when grounded (eg PK Fire)
-Pogo Tail (Down B ? Down air ?) from Super Metroid. Somewhat similar to bowser bomb. Leap forward, come crashing down. Spikes on the tip. Can be used up to three times if re-input slightly before hitting the ground (L-cancelling timing ?) ; the more bounces, the harsher the landing lag
-Sky Drop (Up-B ?) from Brawl and Other M when Ridley grabs Samus and drags her accross the walls. Quickly leaps upwards. If an enemy is within trajectory, Ridley grabs them then throws them diagonaly down and forward (aimable ?). Ridley enters free fall after using this move, even if it hits, as to not make it too strong of an edgeguarding tool. Could also work as a similar move to ganon's side-B. If that's too strong, trajectory could be meteor with Ridley coming crashing behind the enemy for a stomp (as seen in his Brawl boss battle)
Ridley's weak spot in the prime series is always within his mouth, so being dealt more damage in the mouth could be a cool mechanic.
Ganon / Black Shadow
Requested since Melee, so obvious choice. I'd keep the Flame Choke on Ganon and give Black Shadow a different kind of Raptor Boost (PMDT could take inspiration from Ganon and Falcon's side-B customs from Sm4sh for that matter). The Triforce Ganondorf PSA is an excellent base for Ganon in my opinion. His quake punch (he uses it when you get too close to him in OOT) better be part of him !
Skull Kid
So many options for how to build his character as the powers of Majora's Mask are frikkin broad. Here's a couple things that are directly caused by Skull Kid in Zelda:MM, not even including his straight-up attacks from the boss fight (the sniping fire ray would make a perfect chargeable neutral B). Should be a gimmick king and a physics alterer (clone him off luigi to steal his negative zone) as he does weird **** throughout the whole game (teleport horses, turns people into plantmen, crashes planets onto other planets, causes global warming). Give him his solarbeam from his bossfight, obligatory. Could be kinda like Robin's sniper shot from Sm4sh. The exploding Beyblades should be added as well.
Dark Samus
Other superpopular character. Clone her off Samus obviously, but there's plenty of source material to make her into her own character (e.g. as different as Mario n Luigi as opposed to Fox n Falco). Dsmash could be the phazon burst around her from metroid prime 3, neutral B could be a scattershot. How about a mechanic similar to Lucario where she gains a phazon charge over time and can spend it on neutral B to make the scattershot a rapid-fire one, down B for a hyper bomb, side-B for a phazon missle (super quick nuke, kinda like a weaker light arrow (zelda final smash)) and up-B for a phazon grapple which deals fast damage over time as long as the target is tethered (those are all of Samus' phazon-enhancable moves from Prime 3) (Dark Samus can fly but doesn't have a Screw Attack as Samus didn't have that ability in Prime 1 and all of Dark Samus' abilities are stolen from Samus' Prime 1 arsenal).
Pichu Bros
Mostly because I only have a top 4 in popular character requests, and since Pichu just isn't that appealing, I think Pichu Bros. (with Plusle + Minun as an alt maybe ?) would make a great character. With a much higher cieling than ICs, desynced grabs, desynced Thunder and grab-to-thunder would make the Pichu Bros extremely powerful combo beasts and edgeguarders, while still remaining frail from their light weight, average neutrléal game due to poor range and self-damage.
**+0.5** (honorable mentions)
Ray MKIII, he looks kinda cool
K. Rool, self explanatory
Micaiah, moar magic users
Lyn, she looks like a blast to play
Krystal, so much potential through staff despite not being a fanfavorite at all
Any of the Hunters from the Prime series (Rundas, Sylux ?)
**-1** (do not want)
Anything 3rd party, let's not attract any unecessary attention
Characters that I feel would be too generic or too similar to their clone-base to be worth the 700+ hours of development time :
-Paper Mario, except as an alt costume (too bad mario's full amirite)
-Toad
-Young Link, except as an alt costume
-Claus (a clone of a clone ?)
-Ninten (enough with the true clones)
Characters that just aren't that hype, or are too obscure or undesired when compared to the rest of the requested characters to be greeted with anything else than ire by disapointed fans :
-Rawk Hawk
-Slippy Toad (I can't even imagine the flamewar that would follow his reveal)
-Sukapon (what is this even)
-Balloon Fighter (same reasoning)
-Lip, Takamaru, Prince of Sablé (too obscure)
-Tom Nook (everything but a fighter)
-Primid (why not a goomba ?)
...
On a side note, as a Smash rep, how would you feel about a shapeshifting polygon ? Since polygons have no specials, its B moves would randomly transform it into one of the perfect attendance crew (12 fighters from Smash 64) with some level of control. For instance, up-B would shapeshift to Jiggs, Kirby or Yoshi (chars with good special-less recoveries), side-B could go to usualy projectile-heavy characters (Link, Samus, Ness ?), down-B would go to hard hitters (DK, Falcon, Fox) and neutral-B to well rounded fighters (Mario, Luigi, Pika)