SUPER MARIO BROS. 2
The game plays quite differently from almost all other Mario games, but it's inclusion led to a number of features that became staples of the Mario series, including Luigi's higher jumping ability, Shy Guys, Pokeys, Bob-Ombs, and so on.
The game features Mario, Luigi, Princess Toadstool, and Toad taking the place of Imajin, Sister, Mama, and Papa respectively. Each use the exact same abilities, the only differences being their stats such as speed, strength, and jumping ability. The abilities made available to the characters include jumping on top of and picking up enemies and items, an extra-high jump after crouching long enough, digging into the ground, plucking vegetables and items from the ground, climbing vines, and riding around on items or enemies in order to reach out-of-reach areas. They can also access the Starman invincibility for a short time. Most of these abilities could easily be worked into a Super Smash Bros. skillset.
Next, we have six major boss characters to consider: Birdo, Mouser, Tryclyde, Fryguy, Clawgrip, and Wart. As Birdo, we know, will go on to have a larger role in further Mario games, I will say yes now to her inclusion, although her moveset for the time being is limited to moving back and forth, jumping, and firing eggs and fireballs from her mouth. She also stands guard outside of an Eagle Mask shaped Gate, which later comes alive and attacks, meaning it could be incorporated into her moveset.
As for Mouser, Tryclyde, Fryguy, and Clawgrip, we may have our first characters who work better as bosses then characters. I will still hold out as tentative for them, but as this is one of their only games, I doubt they will give us enough to make a full moveset. Mouser is a large shades-wearing mouse who throws bombs. That's about it. Tryclyde is a giant, three-headed serpent who breathes fire at you. Fryguy is a giant ball of fire who spits fire at you and splits into smaller balls of fire. Clawgrip is a giant crab who chucks rocks at you, and who replaced a third Mouser fight from the original game. All work well as solid boss fights, so I think I can be okay with that.
Then we have Wart, the main villain who kidnapped a bunch of fairies called Subcons in order to rule the dream world. For his boss battle, all he really does is spit bubbles at you, which doesn't seem like he then would function as a character, however, Wart has the unique advantage of being the main villain, meaning his moveset can be made up of references to the game as well, and he can incorporate many of his minions into his moveset. For instance, his throne room is decorated with Phantos. All he has to do is make use of them. He also has Bob-Ombs he can throw, Autobombs he can ride and so on. He's not without potential.
Now for our enemy characters. Super Mario Bros. 2 features eighteen enemy characters: Shy Guys, Tweeters, Ninjis, Hoopsters, Pidgits, Beezos, Snifits, Phantos, Trouters, Sparks, Cobrats, Pansers, Pokeys, Ostros, Porcupos, Albatosses, Bob-Ombs, and Flurries. Shy Guys, Snifits, Pokeys, Bob-Ombs, and Sparks are the main enemies that have carried on into later Mario games so its fair to start with them. Shy Guys fall in alongside Koopas, Goombas, and so on as some of Mario's most iconic enemies and have also proven versatile enough to say that they will in fact be included, as even in this game they have moveset potential if you factor in Snifits and Beezos as their offshoots and their ability to ride Ostros and Autobombs. Pokeys mostly just wiggle in place and for now probably work best as obstacles on a desert-themed stage, and Sparks mostly just circle platforms. Bob-Ombs I won't write off entirely as characters, as they do have a few variants in later games, but they probably work best as items. (Dropping from an Albatoss would be a solid entrance animation though).
As for the rest, the main thing acting against them is their lack of appearance in later games. For this game, Tweeters simply bounce forward, Ninjis jump in place or toward the player, Hoopsters crawl up and down on vines, Pidgits ride flying carpets, Beezos fly forward, Phantos come to life and chase you when you pick up a key (they'd be a great stage hazard), Trouters jump, Cobrats jump and spit pellets, Pansers launch fireballs, Ostros give rides, Porcupos crawl, Albatosses drop Bob-Ombs, and Flurries slide around. None of them particularly give you much to work with as playable characters, so for now, no.
Next up are the stages. As they are divided into seven distinct worlds with individual themes, we can easily make a stage out of all seven with not much difficulty. World 1, 3, and 5 are all mostly grassland types, but 5 is set at night, and 3 is set in a waterfall/cave area. World 2 and 6 are also both deserts, so it might be reasonable to combine similar worlds, but seven stages is perfectly manageable, so I don't think there's much need.
As for items, we see the return of Mushrooms, 1-Ups, Starmen, POW Blocks, and Koopa Shells, most of which can perform the same function. We also see vegetables, bombs, timers that freeze time, potions that make doors (because that makes sense), and rockets that carry you higher into the stage. All of these can be easily incorporated.
Now, lets see what we've got!
Characters:
Mario: Jump, Fire Flower, Starman, Axe, Springs, Pick up, pull vegetables, climb vines, super jump, dig, bombs, ride autobomb, ride carpet
Luigi: Echo of Mario, Pick up, pull vegetables, climb vines, super jump, dig, bombs, ride autobomb, ride carpet
Bowser: Jumping, fireballs, hammers, minions
Princess Toadstool: Pick up, pull vegetables, climb vines, super jump, dig, bombs, ride autobomb, ride carpet
Toad: Pick up, pull vegetables, climb vines, super jump, dig, bombs, ride autobomb, ride carpet
Wart: spit bubbles, Phantos, reference character?
Birdo: jump, spit eggs, fireballs, drop crystal ball, Mask Gate
Koopa: Shell Tuck, Shell Spin, Paratroopa Wings, Hammers?
Shy Guy: Beezo wing, Beezo trident, Snifit pellet, ride Ostro, ride Autobomb
Lakitu: Float on cloud, throw Spinies
Goomba: Nothing
Piranha Plant: Bite
Hammer Bros.: Jump, throw hammers
Buzzy Beetles, Bloopers, Cheep Cheeps, Pokeys, Bob-Ombs, Tweeters, Ninjis, Cobrats, and Flurries all tentative
Bosses:
Mouser: Throws bombs
Tryclyde: Breathes fire
Fryguy: Breathes fire, splits into smaller fryguys
Clawgrip: Throws rocks
Stages:
Mushroomy Kingdom
Mushroom Kingdom
Kingdom I
Mushroomy Kingdom (Underground)
Sky Plateau Stage
Mushroomy Kingdom (Underwater)
Fishing Bridge Stage
Giant Mushrooms Stage
Fortress Wall Stage
Bowser's Castle
Sky Stage
World 9 (Weird Stage)
World 1 (SMB2)
World 2 (SMB2)
World 3 (SMB2)
World 4 (SMB2)
World 5 (SMB2)
World 6 (SMB2)
World 7 (SMB2)
Items:
Super Mushroom
Life Mushroom
Fire Flower
Starman
Fire Bar
Bullet Bill
Bullet Bill Blaster
Spring
Poison Mushroom
Vegetable
POW Block
Bomb
Bob-Omb
Shell
Timer
Door Potion
Egg
Rocket
Thanks for reading! Join me next time for Super Mario Bros. 3