by Every time a new Mario spinoff is announced the question is what characters will be playable. So far there's a total of 5 announced.
Mario
Luigi
Wario
Waluigi
DK
Now lets look at the other games in the series to see if there's any characters who show up often.
Mario Tennis 64
Mario Tennis VB
Mario
Luigi
Peach
Toad
Yoshi
Koopa
DK Jr
Mario Power Tennis
Mario Tennis: Power Tour
Mario Tennis Open
Mario
Luigi
Peach
Daisy
Yoshi
Boo
DK
Diddy
Bowser
Bowser Jr
Wario
Walugi
Baby Mario
Baby Luigi
Dry Bowser
Luma
Mii
QR Yoshi colors
Metal Mario
Mario Tennis Ultra Smash
Mario Sports Superstars
Guaranteed
Peach: Peach has appeared in every Mario Tennis game to date and I think it's safe to say that she will be shown in the next trailer
Daisy: Daisy has appeared in every Mario Tennis since her first appearance in the series outside of Power Tour
Yoshi: He's been in every Mario Tennis game
Bowser: He's been in every Mario Tennis outside of the VB one
Boo: Since, appearing in Mario Tennis 64 Boo has been in every Mario Tennis outside of Power Tour and being one of the few tricky characters makes his case that much better.
Rosalina: Rosalina was planned for Mario Tennis Open and since then she has appeared in every Mario spinoff withstanding the huge cuts in Mario Kart 7 and the Top 100.
Bowser Jr: Bowser Jr is really hit or miss when it comes to spinoffs. However, Camelot does value him more then Diddy Kong as seen with Ultra Smash and he's been in Kingdom Battle, Deluxe and played a big part in the Nintendo Switch marketing.
Good Chance
Toad: Toad was dropped for the Mario Tennis series after 64 and did not return until Ultra Smash only to miss the cut in Sports Superstars again and he was also not playable in the Top 100. With that said him being in Ultra Smash makes me think he will return.
Toadette: Toadette was a character put into retirement after Mario Super Sluggers and was not seen until Mario Kart 8 Since, then she has been quite the regular appearing as a playable character in Mario Party 10, Captain Toad and Ultra Smash. I see her being playable if Toad is once again.
Dry Bowser: Dry Bowser always seems to make his way into the Mario spinoffs outside of Sports Superstars and him being easy to make and being one of the few Defensive characters gives him a good chance.
Diddy: While I would say Diddy has a good chance him missing the cut for Ultra Smash makes me think otherwise. With that said fans where unhappy about him not being in that game so I'm sure he will return.
Birdo: Do to Birdo being in the Tennis part of Sports Superstars I say she has a small chance of making the cut even if she is no longer used in Party and Kart.
Unlikely
Baby Mario: Baby Mario was playable back in 64 only to go missing until Open. He did not return in Ultra Smash only to be playable again in Sports Superstars: I say he's only playable if the roster is 20 or more due to him needing a new HD model.
Baby Luigi: Baby Luigi has only appeared in Sports Superstars and he needs Baby Mario to be payable to even get in and an HD model making him even more unlikely.
Sprixie: She is likely a one time character like Fly Guy was. Her being in Ultra Smash does give her a chance though.
Paratroopa: He has not appeared in Tennis since, Power Tennis and that will likely remain the case with how many staples are playable in the series now.
Luma: I only see him coming back if they do double partners again.
Baby Peach: I could see her making it over Baby Luigi again. Though if added on top of the bros I think the roster would have to be at least 25 characters.
Metal Mario: While he could make the cut over Dry Bowser there's already a number of power types.
Pink Gold Peach: Could see her if roster is 20 plus. However I think some other female character would be picked over her.
Fly Guy: Seems like a one time only character.
Mii: I don't see them taking the time to being back all of that Mii gear
No Chance
Shy Guy: Seen as an NPC
DK Jr: Replaced by Diddy starting with Power Tennis
Koopa: Seen as a NPC
Petey: Boss battle
Wiggler: Maybe as a boss battle
Human characters: Too many and no need with Miis being a thing now.
Possible newcomers
Pauline: She could be the SMO character due to the Mario Tennis games also adding in a character from the most recent 3D Mario game.
Cappy: If Camelot does not have time to program Pauline in
Baby Daisy: If the Baby Bros and Baby Peach all make the cut.
My wishlist
Dixie
Kamek
E. Gadd
Nabbit
My roster predication 18 in total
All-Round
Mario
Luigi
Daisy
Birdo
Speed
Toad
Yoshi
Diddy Kong
Technical
Peach
Power
Donkey Kong
Bowser
Wario
Rosalina
Tricky
Boo
Bowser Jr
Toadette
Defensive
Waluigi
Dry Bowser
Pauline
Dream Roster
All-Round
Mario
Luigi
Daisy
Birdo
Dry Bones
Speed
Toad
Yoshi
Diddy Kong
Nabbit
Baby Mario
Technical
Peach
Baby Luigi
Luma
Kamek
Dixie Kong
Tricky
Bowser Jr
Boo
Toadette
E.Gadd
Cappy
Power
Bowser
Donkey Kong
Wario
Rosalina
Metal Mario
Defensive
Waluigi
Dry Bowser
Pauline
Funky Kong
Glydon
Mario
Luigi
Wario
Waluigi
DK
Now lets look at the other games in the series to see if there's any characters who show up often.
Mario Tennis 64
Mario Tennis VB
Mario
Luigi
Peach
Toad
Yoshi
Koopa
DK Jr
Mario Power Tennis
Mario Tennis: Power Tour
Mario Tennis Open
Mario
Luigi
Peach
Daisy
Yoshi
Boo
DK
Diddy
Bowser
Bowser Jr
Wario
Walugi
Baby Mario
Baby Luigi
Dry Bowser
Luma
Mii
QR Yoshi colors
Metal Mario
Mario Tennis Ultra Smash
Mario Sports Superstars
Guaranteed
Peach: Peach has appeared in every Mario Tennis game to date and I think it's safe to say that she will be shown in the next trailer
Daisy: Daisy has appeared in every Mario Tennis since her first appearance in the series outside of Power Tour
Yoshi: He's been in every Mario Tennis game
Bowser: He's been in every Mario Tennis outside of the VB one
Boo: Since, appearing in Mario Tennis 64 Boo has been in every Mario Tennis outside of Power Tour and being one of the few tricky characters makes his case that much better.
Rosalina: Rosalina was planned for Mario Tennis Open and since then she has appeared in every Mario spinoff withstanding the huge cuts in Mario Kart 7 and the Top 100.
Bowser Jr: Bowser Jr is really hit or miss when it comes to spinoffs. However, Camelot does value him more then Diddy Kong as seen with Ultra Smash and he's been in Kingdom Battle, Deluxe and played a big part in the Nintendo Switch marketing.
Good Chance
Toad: Toad was dropped for the Mario Tennis series after 64 and did not return until Ultra Smash only to miss the cut in Sports Superstars again and he was also not playable in the Top 100. With that said him being in Ultra Smash makes me think he will return.
Toadette: Toadette was a character put into retirement after Mario Super Sluggers and was not seen until Mario Kart 8 Since, then she has been quite the regular appearing as a playable character in Mario Party 10, Captain Toad and Ultra Smash. I see her being playable if Toad is once again.
Dry Bowser: Dry Bowser always seems to make his way into the Mario spinoffs outside of Sports Superstars and him being easy to make and being one of the few Defensive characters gives him a good chance.
Diddy: While I would say Diddy has a good chance him missing the cut for Ultra Smash makes me think otherwise. With that said fans where unhappy about him not being in that game so I'm sure he will return.
Birdo: Do to Birdo being in the Tennis part of Sports Superstars I say she has a small chance of making the cut even if she is no longer used in Party and Kart.
Unlikely
Baby Mario: Baby Mario was playable back in 64 only to go missing until Open. He did not return in Ultra Smash only to be playable again in Sports Superstars: I say he's only playable if the roster is 20 or more due to him needing a new HD model.
Baby Luigi: Baby Luigi has only appeared in Sports Superstars and he needs Baby Mario to be payable to even get in and an HD model making him even more unlikely.
Sprixie: She is likely a one time character like Fly Guy was. Her being in Ultra Smash does give her a chance though.
Paratroopa: He has not appeared in Tennis since, Power Tennis and that will likely remain the case with how many staples are playable in the series now.
Luma: I only see him coming back if they do double partners again.
Baby Peach: I could see her making it over Baby Luigi again. Though if added on top of the bros I think the roster would have to be at least 25 characters.
Metal Mario: While he could make the cut over Dry Bowser there's already a number of power types.
Pink Gold Peach: Could see her if roster is 20 plus. However I think some other female character would be picked over her.
Fly Guy: Seems like a one time only character.
Mii: I don't see them taking the time to being back all of that Mii gear
No Chance
Shy Guy: Seen as an NPC
DK Jr: Replaced by Diddy starting with Power Tennis
Koopa: Seen as a NPC
Petey: Boss battle
Wiggler: Maybe as a boss battle
Human characters: Too many and no need with Miis being a thing now.
Possible newcomers
Pauline: She could be the SMO character due to the Mario Tennis games also adding in a character from the most recent 3D Mario game.
Cappy: If Camelot does not have time to program Pauline in
Baby Daisy: If the Baby Bros and Baby Peach all make the cut.
My wishlist
Dixie
Kamek
E. Gadd
Nabbit
My roster predication 18 in total
All-Round
Mario
Luigi
Daisy
Birdo
Speed
Toad
Yoshi
Diddy Kong
Technical
Peach
Power
Donkey Kong
Bowser
Wario
Rosalina
Tricky
Boo
Bowser Jr
Toadette
Defensive
Waluigi
Dry Bowser
Pauline
Dream Roster
All-Round
Mario
Luigi
Daisy
Birdo
Dry Bones
Speed
Toad
Yoshi
Diddy Kong
Nabbit
Baby Mario
Technical
Peach
Baby Luigi
Luma
Kamek
Dixie Kong
Tricky
Bowser Jr
Boo
Toadette
E.Gadd
Cappy
Power
Bowser
Donkey Kong
Wario
Rosalina
Metal Mario
Defensive
Waluigi
Dry Bowser
Pauline
Funky Kong
Glydon
