So I was watching SmallAnt do his zero star run, and he clipped through the 2nd Key Door with the BLJ in the Castle’s Lobby. Wouldn’t that be a time save to do, or would it crash the game if you tried playing Third Bowser?

You can only get upstairs with the 2nd key, there is literally nothing there if you dont open the door cause the loading zone

There are 3 loading zones in the castle, 1: The Lobby and all single doors and star door. 2: The basement with all rooms in the basement plus the star door 3: The Staircase + All upstairs.

You can't clip between loading zones. You will have to get the keys first to get access to the loading zones

upstairs area doesnt load unless you open the door with the key. you can clip behind the door but its a dead end, you cant go up