The quick and dirty of these videos:
1. Catch Mips. See the top video.
2. Don’t grab the star and take him to the door.
3. Walk into the right part of the door and slowly inch yourself closer to the doorframe.
4. The second Mips’ shadow disappears, press and hold Z.
5. Turn around while still holding Z and then stand up and press B. If you timed it correctly, then you’ll grab Mips. If you can’t pick him up, that means you went too far to the right and need to try again.
6. Hold down on your control stick and jump a few times and you’ll get through the door.
7. Repeat steps 3 and 4 for the Bowser door, except you don’t need to grab Mips this time, so the timing is far more lenient.
First video made by: Tristan
Second video made by: mrKerij