Alright guys, get ready for a wall of text. Apologize for my poor grammar, did not have the chance to proof read everything:
Toad - A great deal of injustice ihas been done to Toad. Most of the arguments against him I've seen are fueled more by personal bias than legitimate issues or concern. All that is said of him aside, he has been and still is a large aspect of Mario's history. As a race and as a character. After New Super Mario Bros. Wii re-introduced a playable Toad into the mainstream, and with the Toads set to appear again if New Super Mario Bros. Mii is ever established as a legitimate title, there won't much in our little fungi's way.
BTW, here is photo evidence that the Toad Bros. return in New Super Mario Bros. Mii:
Medusa - With Project Sora coming off of development for Kid Icarus Uprising, it is understandable if the team is sentimental and decides to incorporate some of the content they have spent the past few years working on. I feel the team, along with Sakurai would have no qualms making another Kid Icarus character playable.
Whether it be Palutena, Medusa, both or someone else; I am not sure. Magnus doesn't really appear as much of an option, but I guess this could change depending on his involvement in Uprising and whether he is a character that is given a ticket to return in a sequel? Still, Palutena and Medusa have the most history behind them and I feel will receive more priority because of it. Medusa has a slight edge as she could probably bring something more interesting in terms of design. This would also mean that another villain is within the game, which would benefit another story mode if Project Sora decided to pursue that avenue again. Perhaps with the 3DS?
Ridley - This one doesn't even really need much more of an explanation. I think the Space Pirate leader's time to shine will finally be here. Looking back at Melee's E3 reveal, during the announcement trailer (which was an early version of what would become Melee's intro) I saw the crowd's reaction when the scene of Samus and Ridley battling came up. It sounded as though many people believed this was indicating his status as a playable character. It was something interesting...
An offhand comment, if Ridley is indeed playable I expect him to be one of the very first newcomers shown off.
Samurai Goroh - I'm not really a fan of his, nor is he exactly the choice I would most enjoy from F-Zero. But I cannot deny that he has had a steady stream of support stemming from the Melee days. There were some people that also assumed he'd be playable in Melee because of his appearance in the intro. Here is a hint Sakurai. Next time, give them a name badge that reads "NPC" so we can avoid future confusion.
Another off hand comment. Out of the three NPCs that appeared in Melee's opening. Only Wolf has become playable.
Starfy - This is where I begin to differentiate from the pack. While being an AT can either be a pro or con depending upon whom you ask. I'm not really getting into that discussion here as that is not the purpose..
Starfy has had a relatively extensive history, with 5 titles in total for his series as of now. Audiences overseas are now able to play a Starfy game as his series has begun to expand overseas, which still shows a future. The director of his series has expressed interest in developing a console title as well as more games. He tends to get thrown into the "lack of moves" camp, but just viewing some of his games on Youtube alone will portray his flexibilty versus how he may have appeared in Brawl.
Another common misconception is that Sakurai somehow hold's a juvenile grudge against this series? The truth is, he doesn't. He is a grown man that isn't extraordinarily obsessed or proud so as to hold a grudge over a game that is only similar in difficulty and "cuteness". "What about that Brawl update"? The way I see it, he probably has some vague knowledge of the rumours also. Chances are he was just playing along with it. The biggest thing hurting him at the time was the series not having a presence beyond Japan, now that this no longer appears an issue I see no reason why our cute little yellow fellow cannot join the rough tough pink puff?
Roy - This one will probably be more controversial. It doesn't appear that we are going to see another Fire Emblem title soon. They have been redoing the Marth saga for the DS and recent comments by members of Intelligent Systems have pointed towards the next new title being a joining of forces between various existing characters throughout the series. This benefits Roy considerably.
As of now every playable character has been a lord, as they are usually the characters that receive the most story and character, obviously. Roy was and still is considered one of the more popular lords. With his game being considered one of the best. So other characters such as Caeda, Sothe, Black Knight, and Micaiah are hurt by this. Only Caeda stands as the most viable option for a non-lord character.
I've always perceived Mewtwo and Roy as being victims of "priorities". Sakurai had probably intended for them to be playable, but was unable to for various circumstances. Whether or not Sakurai has any interest in bringing back either is unclear. But Roy has the least opposition compared to that of Mewtwo.
Fun Fact: Before Brawl was released many people reported hearing the track "The Kingdom of Bern" on Castle Siege, This track appeared in numerous demos but was mysteriously dropped in the final release.
Little Mac - Along with Pit he has always been a retro character with a lot of support behind him. Although Little Mac has an advantage this time, his series was revived prior to the next Smash Bros (Punch Out!!). On top of that there is a possibility of him having a future as the developers (can't remember who at the moment) have expressed an interest in developing a sequel. So this is a character I cannot see why he wouldn't be able to be playable unless Sakurai deem's him too "punchy" or something along those lines. But given how most characters movesets are only loosely based on their series anyways, I don't think it is as much of an issue as I have seen some portray it.
Saki Amamiya - This one is a little bit tougher, because he does have some things holding him back. Right out of the gate I'll begin with his biggest obstacle, that is his series. His series, out of most all of the series in the game, is among the smallest and least selling. His being an Assist Trophy probably had much too do with the fact that the original 64 title was available only to Japan. So during the time of development they could have been implementing him without knowledge of it's release on the Virtual Console (though I doubt this). Which, the Virtual Console title did sell well overseas. It was because of the sales of the VC title that Treasure even decided to go to Iwata and ask about developing a sequel (Sin and Punishment: Star Successor). To which Iwata allowed them to develop.
Being in Brawl has probably helped him the most out of any character. Even for people who have never played Sin and Punishment, they will be able to loook and Saki and say "wasn't that that guy from Brawl? That trophy thing?". In fact they put so much detail into his AT that Sakurai was practically teasing how playable he looked against the other characters. Also admitting he had been a popular request in Japan. Now with Saki having fans beyond the border of Japan, coupled with those same fans that made him a popular request to begin with. Sakurai may decide to go ahead and flesh him out. Possibly even integrating some elements of the sequel into him.
Shulk - Shulk is an interesting choice to me. He isn't one who get's a lot of attention, but yet comes up every now and then. There isn't much I can say outside of I just see Sakurai gravitating towards this title and want to represent the "Wii RPG trifecta". Xenoblade has become the new "Earthbound". What I mean by this is that it is another Nintendo RPG that the core fans are very rabid and very vocal. If Western gamers put their money where their mouth is (yes I think eventually North America will see a release) I see him being one of the more surprising additions.
Mii - Love them or hate them, they are here to stay. Say what you will but the Mii is Nintendo's largest promotional icon they have at the moment. Only three characters in Nintendo's history have transcended pop culture, and those are Mario, Link, and Pikachu. Add Mii to that list now.
But that raises the question, can Mii be considered a character? Want to know my honest answer? I don't know and I really don't care. I'm not going to rack my brain trying to come to some mental understanding of what exact window Mii falls under. All I know is if the thing is good enough for Mario Kart and other titles, it should be good enough for Smash Bros. The one problem is this comment:
"Of course, I think there was a possibility of taking Smash Bros. in a more casual-gaming direction. For example, we could make the art style simpler or make it possible to use Miis. However, with the various titles that the Wii was to offer, I felt that people were looking for something different. That’s the reason I decided in very early stages of development that the Wii pointer and motion movements would not be a primary feature of the game."
Is it possible Sakurai may end up finding a way to incorporate them? He may. But we will just have to wait and see.
Mewtwo - I know we are going to get an inevitable 5th Generation Pokémon. Whether it is Zoroark, Victini, Pokémon Trainer style N or even N riding on the back of Reshiram. I have no idea what to expect, but I do hope for one thing. That is for Mewtwo to return.
To be honest this character hasn't ever lost popularity. I can talk to 20-something year olds who have never touched a Pokémon game in years yet they can recall Mewtwo and how cool of a character he was. Over at IGN they held a massive Pokémon poll where, they claim, 14 million votes (though taking into consideration multiple votes lower that, but even if you assume on average a vote was cast ten times it would still leave you with 3-4 million votes) were cast. Placing second in this poll was Mewtwo, only beat out by Charizard. So I think the issue of popularity is moot.
The problem he faces comes from the issue of how high will they go wtih Pokémon characters. Pikachu and Pokémon Trainer are staying, A 5th Generation character is inevitable, Jigglypuff will likely stay. Lucario is the only Pokémon in a tough spot, he has the chance of staying or leaving. In an ideal world no one would be cut and we could include both a 5th Generation character as well as Mewtwo. Saying this usually invokes of a response of "that is too much" or "the first generation is over represented". Let me talk about those two complaints.
1: Too many
Who defines this? I mean really are there caps that I was not aware of? Is it impossible for the development team to work on multiple characters at once? When you break it down this argument is quite silly and goes to a fundamental problem with people when the topic of characters arise. They see the roster like we see The House of Representatives. There is nothing to substantiate this as, on the contrary, Sakurai has indicated more towards looking at characters themselves and not "collectively".
2: Over Represented
Again, who defines this? The only thing we are certain of is that Game Freak and The Pokémon Company will push Sakurai for a 5th Generation Character and content. That is it. HeartGold and SoulSilver will likely be represented in a stage and other things. So character wise it is a non-issue. People assume that every generation HAVE to be, but that is something that is neither necessary nor true.
In addition they seem to forget that a playable character is not the only way to represent things. The largest representing entity of Pokémon in Smash Bros are the Pokéball Pokémon.
Mewtwo, along with Roy, was likely also a victim of "priorities". We don't know that to be the case but there are little pieces that point to that. Outside of that, though there are a few more obstacles in his path. There really is no valid reason he should not return, even if we keep everyone from Brawl.
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Only characters left needing a write up are Warioware character (leaning towards Orbulon at the moment) and Paper Mario.