Koopa in Koopa Cruiser (room 313)
Here I will explain the NPC clip the best I can so others can understand it:
NPC ejection
Ejection to the right:
Be inside the NPC,
have the same X-pos or more, as the NPC,
walk left
Ejection to the left:
Be inside the NPC,
have less than the X-pos as the NPC,
walk right
Most standing NPC don't eject at all.
Walking NPC will eject for 4096 usually (which equals 0x100 in hex).
Very few NPC will eject for more. The Koopa in Koopa Cruiser will eject for up to 5120.
How to get inside an NPC
Jump into the NPC from above or keep switching places until the NPC has walked inside you.
It's very tricky and not feasible to do on real-console.
However, the Koopa in Koopa Cruiser will never change direction, so it is very easy to do the clip even on real-console. You just need to start switching places at the right time, and you need to be positioned from the wall perfectly (this will be explained below).
Wall clipping
To wall clip, you need to be ejected more than 4096 units.
You can only clip rightwards or leftwards so far.
You need to be positioned near the wall perfectly:
Too close, and you will be ejected less than 4096 no matter what.
Too far away, and you will be ejected for 5120(or whatever the maximum the NPC ejects for) and still not be in the wall.
If you are between 4096 and 5120 from the wall, you can be ejected into the wall.
If you are with 2 brothers, the back brother cannot enter the wall as far as I tested.
If you are with 1 brother, you can clip through, however.
For the GIF above:
The 2 brothers are positioned exactly 4096 from each other, if you walk horizontally.
So if you walk away from the wall so the 2 brothers are aligned horizontally, and then walk for 1 additional frame, you will be ~4600 units away from the wall. Since the Koopa ejects for ~4900, the clip happens.
Other "more than 4096" NPCs
There are only very few I found.
These work but they never approach a wall...
- The captain in the Teehee Valley ship
- Walking Yoshi in the Yoshi theatre
- Koopa in the end room of Koopa Cruiser
These work and the wall clip can be done
- Fat lady in the relaxation room
-
Oho Jee
Luigi in the beginning of the game is special because he is a scripted NPC who does stuff based on your position and movement. As far as I've seen, he is the only NPC that can eject you vertically when walking into him (
Luigi clip).