I think this was already debated. The difference between the Mario series and the others like FE and Zelda.
Now unless this was the only Alt costume possible for Zelda, like Dr. Mario for Mario, Mr.L for Luigi, Dry Bowser for Bowser, and Shadow Queen for Peach(Yes, all of them, you can't think of anything else for their corresponding characters)
I hadn't seen it being debated, this thread moves faster than Usain Bolt at times, so I miss things every now and then.
As for possible costumes for the Mario cast (I'm not arguing that most of these picks are the best choices, but they're possible nonetheless) - there are plenty of options apart from the ones used:
Mario:
- Sunshine costume
- Any of his five Mario Party 2 costumes (Pirate, Cowboy, Astronaut, Explorer, Wizard)
- Striker Mario (Mario Strikers Charged)
- Any of the power-ups he can use
- NES Golf Outfit
- Mario's Tennis Outfit
Luigi
- Any of his five Mario Party 2 costumes (Pirate, Cowboy, Astronaut, Explorer, Wizard)
- Parade Luigi (Paper Mario ending)
- Striker Luigi (Mario Strikers Charged)
- Any of the power-ups he can use
- NES Golf Outfit
- Mario's Tennis Outfit
Peach
- Sunshine dress (minor difference, but different nonetheless)
- Any of her five Mario Party 2 costumes (Pirate, Cowboy, Astronaut, Explorer, Wizard)
- Sport Suit Peach (Mario Sports Mix)
- Nurse Peach (Dr. Mario)
- Short Dress Peach (Mario Power Tennis, also used in Golf) - different version in Mario & Sonic at the Olympic Winter Games
- Striker Peach (Mario Strikers Charged)
- Motor Peach (Mario Kart Wii)
- Wedding Dress Peach (Super Paper Mario)
Bowser
- Wedding Suit Bowser (Super Paper Mario)
- Any of his Mario Party 2 costumes (Wizard, Pirate)
- Armored Bowser (Yoshi's Safari)
- Dreamy Bowser (Mario & Luigi: Dream Team)
- Striker Bowser (Mario Strikers Charged)
- Rookie