Actually, that's a good question... If you could pick eight partners or supporting characters from the entirety of the Mario RPG series (PM, M&L, SMRPG) to become Mario's partners in a new game, who would you pick? My list would be as follows:
1) Geno (obviously)
2) Mallow (obviously!!)
3) Jonathan Jones
4) Vivian
5) Parakarry
6) Prince Peasley
7) Dreambert (shhh I think he's adorable)
8) HECKING LUIGI
A new game with all the fan-favorite characters, where Mario has to save the entirety of time itself from a new threat? That new threat takes control of all previous Mega-Villains, and the final boss feels like you're almost fighting yourself, because they have as many partners as you do?
SUPER MARIO RPG 2:
PLUMBING THE TIME-SEWERS
Mario joins up with old friends as they help him take on his biggest threat yet, featuring:
1) Geno
-First joining your party to alert you of the threat, Geno makes his grand return from Super Mario RPG! In addition to being very strong in battle, he can call on the power of the stars to reveal nearby secrets, and helps remind you of your next goal.
2) Starlow
-After hearing the story from Geno, you head to Peach's castle to get her help- only to find she was kidnapped again... After saving Starlow from some of Bowser's baddies, she helps you, and even fights with you for the first time! She can tell you about an enemies health and weaknesses, and also tell you about whatever location you're in.
3) Mallow
-Obviously, being what Geno is most familiar with, the first place the party goes is back to the Mushroom Kingdom, right after Smithy was defeated. It turns out, whatever force is messing with time immediately brought him back, and is ruining everything. As you try to stop Smithy for the second time, you find King Mallow, who happily joins your party to kick Smithy's tush again. He's an adept user of magic, and in the overworld he can use his control over the weather to help solve puzzles by watering plants or reversing the wind. He can even help Mario descend more slowly with a cloudy platform.
4) Vivian
-After defeating Smithy once and for all, the second time, the next item on the agenda is one of the most dangerous- the Shadow Queen is back! Feeling a bit guilty due to her relation to said Queen, (and also because she has a massive crush on Mario,) Vivian joins your party to help out. She's a master of the shadows and fire. In the overworld, she can help you hide and protect you from anything, as well as use her powers of fire to burn down obstacles.
5) Nastasia
-Surprise surprise, Dimentio has been given power once again, and with Count Bleck and Tippi gone to live happily ever after, Nastasia offers to join your party as the strongest secretary around. Her hypnotic abilities make it easy for her to strengthen Mario and his friends, as well as make opponents weaker. In the overworld, she can hypnotize enemies to keep them from attacking you, or use her strong psychic powers to lift heavy rocks Mario can't break with his hammer.
6) Broque Monsieur
-The pattern continues with yet another super-boss from before given power once again. Dark Star Bowser threatens to take over the Mushroom Kingdom, so this French Block-Man comes to help. He's nearly indestructible with his high defense, and has his pets to deal serious damage. On the overworld, he can act as a bridge across gaps by using his blocky body, or shield you from nearly anything.
7) Yoshi
-As you get close to realizing who the true threat is, you have to go WAY back- back to when Mario was a baby- and find out that Kamek has stolen Baby Mario AND Baby Luigi! Obviously, the Yoshi tribe that worked so hard to stop that from happening is out with a vengeance to get them back. Working with Mario's adult self, whichever color of Yoshi you decide to partner with can help you out by throwing eggs at hard-to-reach places, or just helping you travel much faster.
8) Cappy
-In the near future, you finally find out what's going on- Bowser has managed to build a time machine, and is trying to rewrite history so he's on top. A slightly older Cappy finds you in this future. He can't be your hat anymore, but he can certainly be helpful! He can be tossed to get far-away items that you can't reach like a boomerang, or even possess certain creatures to use their abilities!
The final boss, of course, is Future Bowser, and he's got a Dream Team of his own. Mr. L, Fawful, Queen Shroob, Beldam, Kammy, Antasma, Wart, and even Waluigi are all on his side! Not to mention the Koopalings and Bowser Jr... But if anyone can do it, it's Mario and his friends!
Coming... never. Unfortunately.