Okay, I think I found the true sequel to Super Mario 64, and that is Super Mario Sunshine. Think about it, Super Mario 64 takes place in Princess Peach's Castle, and all of the courses (except Rainbow Ride) are portels. In Super Mario Sunshine, the first few courses are portels. In might have been based on SM64. Also, do you remember the quote, "Wow! Another Power Star! You're gaining more power to the castle!". Well, in Super Mario Sunshine, the Shine Gate gets power from the Shine Sprites. They could've been based it on SM64 also. Also, I think that New Super Mario Bros. is the sequel to Super Mario Sunshine. In the ending to Super Mario Sunshine, he wants to fight Mario again when he's bigger. Well, 4 years later, captures the princess, and now he fights Mario more often. Alot of rumors say that:
Luigi's Mansion could be a sequel to Super Mario Sunshine because Mario could've been abducted by King Boo after his vacation.
That's not true because Luigi's Mansion was made way before Super Mario Sunshine.
Super Mario 64 DS is the sequel to Super Mario 64.
Not true. It's still a remake even though it has some big changes.
Now you maybe know.