Heres my Idea, There will be 16 stages (Each with 4 Levels (With the exception of Planet Zebbes, which has 5)) This adventure mode will Have Mid-Bosses of enemies (or in this Case, Predators)
Stage 1 Mushroom Kingdom
1-1: Reach the Goal
1-2: Reach the Goal and defeat the TowTow
1-3: Find all of the Mushroom Keys and then Defeat Mario
1-BOSS: Defeat King Bob-Omb
Stage 2: Kongo Jungle
2-1: Reach the Goal, and defeat Giant Donkey Kong
2-2: Reach the Goal and Defeat General Klump
2-3: reach the top of King K. Rools Castle
2-BOSS: Defeat King K. Rool
Stage 3: Underground Maze
3-1: Reach the Goal and Defeat Link (Green, Red, Blue Yellow, and Black Color)
3-2: Reach the Goal and Defeat Toon Link
3-3: Reach the Goal and Defeat Ganondorf
3-BOSS: Defeat Skull Kid
Stage 4: Planet Zebes
4-1: Reach the Goal and Defeat Ridley
4-2: Reach the Goal and defeat the Roturret
4-3: Find the Path to Mother brain
4-BOSS: Defeat Mother Brain
4-5: Escape Planet Zebbes
Stage 5: Dream Land
5-1: Reach the Goal and Defeat Kirby
5-2: Reach the Goal and Defeat Bonkers
5-3: Reach the Goal
5-BOSS: Defeat Kracko
Stage 6: Green Hill Zone
6-1: Reach the Goal
6-2: Reach the Goal and Defeat Sonic
6-3: Reach the Goal
6-BOSS: Defeat Dr. Eggman
Stage 7: Parrallel Universe
7-1: Defeat Ice Climbers
7-2: Defeat Duck Hunt Dog
7-3: Defeat Mach Rider
7-BOSS: Defeat Duon
Stage 8: Pac-World
8-1: Reach the Goal
8-2 Open a Portal to the Netherworld
8-3: Defeat Pac-Man (If the Player is Using pac-Man in his default Pallet, Then Pac-man will use a red pallet)
8-BOSS: Defeat Betrayus
Stage 9: The Plain
9-1: Reach the Goal
9-2: Reach the Goal
9-3: Reach the Goal and Defeat Poppy bros. Sr.
9-BOSS: Defeat Wiggler
Stage 10: The Wilds
10-1: Reach the Goal
10-2: Reach the Goal and Defeat Boom Boom
10-3: Defeat Saki
10-BOSS: Defeat General Guy
Stage 11: Wily Castle
11-1: Reach the Goal
11-2: reach the Goal and Defeat Spaak
11-3: Reach the top of Wily Castle
11-BOSS: Defeat Dr. Wily
Stage 12: Lake of Rage
12-1: Reach the Goal
12-2: Defeat a hoard of Pikachus
12-3 Defeat Giant Pikachu
12-BOSS: Defeat Rayquaza
Stage 13: The Beaten Road
13-1: Reach the Goal
13-2: Defeat Ness and Lucas (A Random ally is chosen, If you Play as Wario, Then Waluigi will be his ally, and Vice Versa)
13-3: reach the Goal
13-BOSS: Defeat Erwin (From Pac-Man world 3)
Stage 14: Wumpa Island
14-1: Reach the Goal and Defeat Crash bandicoot
14-2: Reach the Goal and Defeat Dr. Neo cortex (He is a predator in this game)
14-3: Reach the Goal
14-BOSS: Defeat Dingodile
Stage 15: Battlefield
15-1: Defeat the TowTow, General Klump, and Roturret
15-2: Defeat Bonkers, Poppy Bros. Sr., and Boom Boom
15-3: Defeat Spaak and Dr. Neo Cortex
15-BOSS: Defeat the Giga TowTow
Stage 16: SubSpace
16-1: Reach the Goal
16-2: Reach the Goal and Defeat a Metal Character
16-3: Find the Generators that reach to the Final Door
16-BOSS: Defeat Tabuu