Fighter from already repped 3rd party franchise
Chance: 50%
This is going to take a lot of explanation, so take a drink, sit back, and enjoy the crazy ride of speculation.
First, I want to say that I think it's possible we will get a 2nd unique third party character from one of the already repped series. It looks like we won't get anymore echo fighters and in that case if we are getting more third party characters from the same series, they would be unique. So far we have no precedence for this as the second reps for third party series (Richter and Ken) are echo fighters. But we do have 3rd party fighters that have merit to them, to the point where they could set a precedence.
These fighters below are ones who I think could break the mold. These are characters who are either iconic, highly requested, important to their series, and/or have something else significant to offer to Smash. Keep in mind this is not an exhaustive list as there are just so many characters that fall under this topic and I don't want to be here all day.
1. Chun-Li - One of the most iconic female characters in gaming. She would have a fun and unique moveset and Street Fighter is big enough that it more than deserves a 3rd rep that is unique.
2. Alucard - Highly requested and almost became playable. There is more than enough new Castlevania content that he would bring to justify a challenger pack.
3. Sephiroth - FF7 just got a a remake and he is highly requested. With the lackluster content FF has, I can see Sakurai going back to add more FF content. Of course there is also other FF characters including from other games like Terra Branford.
4. Raiden - In
this fan poll done just last year, Raiden actually did very well in Japan and even beat 2B and Sephiroth, two highly requested characters, so this says a lot. Raiden is a major character in the MGS games and is the type of character that not many talk about, but he does make sense to be a character....just like most of the third parties in the first pass.
5. Any Sonic character - Really, this should have happened by now. Sonic is THE third party character in Smash. The fact that we've gone this long without a second character is head-scratching. Even with Tails and Knuckles dead and skinned, we got Shadow and even if assist trophies are deconfirmed we got Dr. Robotnik, the main villain of the series and he is one of the most iconic villains in gaming.
6. Zero - Highly requested and is a big part of the franchise. Yes he is an assist trophy but come on people don't make me bring up my big post on assist trophies.
So clearly I'm confident in the above people.....so what's with the 50% chance? Well I've already brought it up but despite the fact that Sonic has been in 3 (4 if counting Smash 4 as different games) games, he still doesn't have a second rep when there are plenty of good candidates with juicy moveset potential and there's plenty of content that isn't in Smash. This combined with the fact that we have gotten many DLC characters and third party characters at this point when none of them are a unique secondary rep, puts this whole topic into question. You could argue that Sakurai has just been busy putting in the big third parties and the ones he's attached to first, but the problem with that is there are characters like Chun-Li and Alucard who are big and important. Not to mention there are still notable third party characters who aren't in Smash yet that Sakurai might prioritize in order to represent more series and grow relations with other companies. Not to mention the fact that ARMS likely indicates there will be more first parties, which automatically lowers the chances of third parties in general.
So overall, yeah I'm mixed on this. When it comes to this topic, there are plenty of characters who have a reasonable chance and they have good reasons to be included over new third parties. But the ambiguous nature of this pass makes me question if this could truly happen.
Want: Abstain
This is really broad and I've given the aforementioned characters a multitude of different want scores so there is no way I can pinpoint an exact score.
Prediction: Rex - 60%
Noms: Ezio (Assassin's Creed) x10