Perspective EditYou probably need to change your menu type to the binary numbers menu in order to make the shadow appear (at least, this was the only way it worked when I did it). To change your menu type you need to go to the computer world, go the button in the bottom right corner and interact with it. If it does not work with changing your menu type, just try very often.
More feats coming soon... Edit
Talk to the boy in Glitch World (the place where you find the Glitch effect) with the Glitch effect equipped.
Complete all 9 levels of ZapNef (the computer game in Itsuki's home)
Complete 10 tests at the testing area. The way to the testing area: Nexus -> Space World (the place where you find the wrench; here you need to find the solar system, go to its right side and go upwards until you see a warp field, step on it and interact with it) -> Sun and Earth (here you have to go to the other warp field) -> Testing area
Complete all twenty tests at the testing area.
After having completed all tests you will be able to go to a new room in the testing area. You will find two warp fields in this room. The one to the left takes you to the first chamber of the testing area, enabling you to come back to this room later. The one to the right only works if you have the lab coat equipped (there is a picture of it on the wall). It takes you to a pink figure. By interacting with it you become able to fly a spaceship. Crash it into a planet or meteorite. (Maybe this is not necessary but it is the way I got it)
Use the wrench to smash the crate in the Pink maze (the place where you find the candle holder).
Go to the art gallery [Nexus -> Doodle World (the place where you find the Doodle effect; interact with the flashing figure below the musical staff) -> Blur Path (just go forward) -> Art gallery]. In its most northern room there is a black entrance. By entering it you can reach a room with black tiles on the floor. Interact with all tiles using the Blob effect.
Go to the tubes (the place where you find the television effect). Find the little pink round kawaii creature and hit it hard.
After having done what was necessary to get the Oxidation feat go and search around. In one room you will find a broken tube you could not enter before.The way leads to a red room with a television (it might be necessary to interact with the broken tube in the right wall which will make strange sounds afterwards). Interact with the television and you reach the Hexagon World where you will soon be chased by two hexagon monsters (you will probably need to try to go get this feat several times because they will keep following you very fast) . Go several steps right and up. You will see a shadow. Interact with it.
On the seabed (close to where you get the Diving suit) you have to go the right side and look around. You will find a place where there is a colourful glowing hole in a wall. Interact with it.
Go to a subway station (one of the many light green entrances in the dream world) and enter. Keeping going right beyond the last station which has a sign in its circle. Exit and leave the subway station. Enter the darkness.
Drink the 45N-Drink at the smiley store in Edible world (the place where you find the Tomato effect).
Go to the Dark World. Go right and you will see several bloodstains. Go right until the bloodstains end, then go up. After some time you will see two black pillars. Most of the time, there will be a stone between those pillars. Either you need to try very often or it is connected to changing your menu type so there is a sunset background in the Computer world (when I tried this way the second time, it did not work so maybe it is not true). If there is no stone between the pillars, go through the way between them and keep going. You will see a house. Enter it. (Getting this feat unlocks a red and black menu type)
Hit the boy who gives you the Nerd effect.
Go to the Ice world and put your raincoat on.
I am not sure about this one yet because sometimes it worked, other times it did not, so it might be connected to chance. What I write here is what I did and saw. Go to Alphanumerical world (the world accessible from the Nexus which is full of letters and numbers). Go to until you see the "word" HUE on the floor, then go right until the end of the "word" WWWWWWW..., then go up. Enter the black hole in the wall and walk the path behind it.
You will come to a place which changes it appeareance if you touch objects while its structure remains the same. There are three sick smiley people. Find and heal all of them. Afterwards keep touching objects until your screen turns green before the landscape appears.
Now there is the part I am not sure about. I walked around, found Easter eggs and tried.to interact with them. Apparently, nothing happened. When I went to the bigger one of the two lakes I saw a red torii (japanese gate to a Shinto shrine) and entered. Another time I could not find Easter eggs or the red gate but found a green gate when I came to the lake while the place was in the state you find it first. While I found only these entrances Jojogape's map shows you can enter from all four states.
You will reach a place with a white frame on a black background. Walk around and you will find pictures which you have to fit into one of the frame's gaps by walking around (there is only one which is right). Do it with all four pictures you find.
Interact with the little orange round guy from the ZapNeF game in the Glitch world (the place where you find the Glitch effect) while having the 8-bit effect equipped.Then go to the end of what you will find.
Interact all with all pink fulgurites in the desert. You come to the desert by the seventh subway station or through Data World (the world full of binary numbers and warp fields)
Go to Purple Polka Dot World (the world where you get the scooter effect). Follow the orange path to the sewers. Enter the black hole in the corridor with the cockroach. The way will leads to a graffiti next to a ladder. It says "SLEEP". If it has no colour wake up and try again. If it is green interact with it. Walk the path which appears. Use the scooter to be faster. Do not get caught.