Basically, this is SUPER AU-Mario. There's all the places from Super Mario RPG, SMB3, SMW, Yoshi's Island, ASMT, ASMBXT, A2XT, etc.
It takes place shortly after SMB3 - when the Koopa Kingdom successfully invaded the Mushroom Kingdom and set up puppet governments in the various states, including a new central Koopa government, and then promptly lost them to Mario, being pushed back to their own territories. It is during the events of ASMT, so King Charles the Fourth has not yet been overthrown.
Here is a brief overview of the various countries:
The Mushroom Kingdom
- Grass Land
Desert Hill (our heroes began their adventure here)
Sea Side
Big Island
The Sky
Iced Land
Pipe Maze
Former Castle of Koopa
The Koopa Kingdom (Broken into 7 fiefdoms controlled by local feuding lords who pay tribute to a central state and each have primacy over several areas of the infrastructure)
- Iggy Koopa's Domain
- Science and Engineering
Industrial Design
Larry Koopa's Domain
- Magical Research
Transportation Manufacturing
Lemmy Koopa's Domain
- Agriculture and Fishing
Logging
Ludwig von Koopa's Domain
- Electricity and Power
Textiles and Clothing
Roy Koopa's Domain
- Industrial Manufacturing
Military
Wendy O. Koopa's Domain
- Luxury Items
Intellectual Capital
Morton Koopa Jr.'s Domain
The Glorious Capital
- Military Intellectual Capital
Bureaucracy and Governance
Dinosaur Land - The SMW Island, under struggle for dominance by various cultural and military influences
- Little Yoshi's Island
Donut Plains
Vanilla Dome
Twin Bridges
Forest of Illusion
Chocolate Island
Valley of Bowser
The Star Realm (the Super Mario RPG Kingdom) - also under struggle for dominance by various cultural and military influences
- Little Mushroom Kingdom
Bowser's Dominion
Booster Tower
Seaside Town
Tadpole Pond
Rose Town
Moleville
Nimbus Land
Barrel Volcano
Land's End
Star Hill
Sunken Ship
ASMT Land - Under the Tyrannical Ideological Rule of King Charles the Fourth
- ASMT Beach
ASMT Forest
ASMT Skies
ASMT Plains
ASMT Underground
ASMT Tundra
ASMT Desert
King Charles the Fourth's Domain
The Castle of Absolutely no Significance Whatsoever
Yoshi's Island - Not broken up into states or districts, except vaguely by the minimalistic Yoshi government. A small part of the island is controlled by the Koopa Kingdom
- Grassy Plains Territories
Rocky Mountain Territories
Jungle Territories
Sunset Hills Territories
Icy Mountain Territories
Bowser's Island Kingdom (now under the control of Bowser Jr.)
Other Planets
- Easy Peasy: Planet of the Cheezy
The Planet of Preventable Forests
The Beach Episode Planet
Colonial Seattle
Mantreol
Anti-Nirvana
Technically not a planet just a ball of atmosphere
The Planet Of Non-Diurnal Content