This is a random fun one but one of my most wanted characters that almost certainly wouldn't go over well with the general fanbase, if anyone, is Sokoban - the titular "Warehouse Keeper" himself.
I think by pretty much any metric he "deserves" to be in, not only based on the long history and huge number of games, but cheekily representing the oft-maligned style of puzzle his series more or less introduced into the wider gaming playbook (Zelda, Pokemon, countless other mainstream / Nintendo games have Sokoban puzzles - not to mention the countless riffs on the concept throughout the years including indie stuff like Handshakes and Baba Is You). It's also a scientifically interesting game in terms of researching...things that are way above my pay grade.
Mechanically the idea might sound like a dead end but if you broaden the scope to include common mechanics introduced in variants of Sokoban on top of the main box-themed stuff, there's a ton of potential. Just a rough idea:
Neutral Special - Box Placement
There's three types of boxes that you will place in a set order (think: how Sora cycles through his spells or Olimar's Pikmin have to be "used" to cycle through the types): Wooden Box, Ice Block, and Metal Crate. The boxes are used via...
Side Special - Box Push (Not Pull!)
So this is like a command grab - the animation is him reaching out and moving forward as if to grab and push a box. If it hits an opponent you just grab them like a normal grab (albeit a longer reach). If it connects with a box, however, it...pushes it. Wooden Crates are light, being pushed the fastest, and will damage opponents a low to moderate amount if caught in the pushing path. Ice Blocks will slide until hitting something (at which point it will shatter and inflict freeze) and leaves the floor temporarily icy (slippery) as it passes over it. Metal Crates are bulky and can't be broken by attacks, but if you manage to push one into someone despite the slow push speed, it's big damage and knockback. All boxes can be pushed off of ledges and will react appropriately (Wooden breaks, Ice continues to slide along the new surface, Metal lands with a thud). Boxes can obviously also serve as cover etc.
Up Special - Teleport Pad
Sokoban places a teleporter pad on the ground where he's standing (or drops it below him if he's in the air). A second use will have him drop/place a second teleporter pad below himself, activating the link between the two pads and swapping the positions of whatever is currently on both of the pads. Usually this will just mean teleporting yourself back on-stage, but creative use can have you teleporting opponents off-stage, teleporting boxes around (including to a mid-air position to then plummet down upon foes), etc.
Down Special - Undo
Takes the quality of life feature found in most decent Soko games and interprets it quite literally, as a full-blown Braid-style rewind. Hold down Special to "rewind" your actions in reverse - i imagine this would have to have a pretty strict time limit, but could lead to crazy mix-ups and a lot of weird tripped out plays. This is a move that would have to be implemented carefully but could become the key to making the character shine.
Final Smash - Payday / Retirement
Sokoban has finally saved up enough money to buy the hot rod he's had his eyes on (as seen in Super Sokoban) and he, I guess, runs over foes, launching them into a cinematic of them being overwhelmed and trapped by boxes in a warehouse as he cruises off into the sunset - or something. I dunno.
Realistically, Lolo would be a more digestable and likely representative for this genre. But a man can dream.