Easter Eggs

In the debug builds of the game, YandereDev has included some Easter Eggs. These are usually added when YandereDev does not have enough time to write code for the game. They include wearable accessories for Yandere-chan, game modes, a small timed event at the starting menu, and a transparent figure/phantom. The final game will have cheat codes that change the appearance of the characters, like the Easter Eggs do.

Accessories

 * "H" key to cycle through hairstyles.
 * Her default hair; which is a ponytail
 * Right-sided ponytail
 * Left-sided ponytail
 * Pigtails
 * Osana Najimi's pigtails
 * Three ponytails
 * Longer pigtails (known as twintails)
 * Drill-hair (or tornado-hair)
 * Long hair
 * Very long hair
 * Rei Ayanami's hair (Neon Genesis Evangelion)
 * Yuno Gasai's hair (Mirai Nikki)
 * Korra's hair (Legend of Korra)
 * Short blonde hair (Galo Sengen)
 * Hatred Mode hair
 * Info-chan's hair
 * Pippi Osu's hair
 * Bald with Barcode (Hitman)

Modes
By using the "?" key, you will see the "Easter Egg Menu". This shows the following options:


 * "P" key to activate "Punished Mode". This mode cannot be deactivated until you reset the game. This mode is a reference to the game Metal Gear Solid 5. It gives Yandere-chan a torn-up version of the original Akademi High outfit, a tan-colored scarf, a black eyepatch on her right eye, a red left arm, a scar on her left eye, a black protrusion from her forehead, a black glove on her right hand, and a cigar. It also replaces the music with "Nuclear" by Mike Oldfield. You are able to press 'D' to disable the copyrighted music.
 * "X" key to activate "Slender Mode". This mode makes Yandere-chan's uniform turn black/gray, her skin will turn completely white, make her eyes blank, and her body shape will resemble that of Slender Man's. Suspenseful music plays the whole time while in this mode. Activating this mode sets Yandere-chan to minimal sanity level, and will cause other students to treat Yandere-chan just as if she were insane. Being noticed by Senpai or by a teacher will result in Game Over. The weapon she chooses becomes larger. You can still laugh to gain sanity in this mode.
 * "B" key to activate "Bancho Mode". The mode cannot be deactivated until you reset the game. This gives Yandere-chan's bandaged arms, a black school outfit, a Sargent cap, and a pick in her mouth. The music playing in this mode is "BafBaf! Sonna ni Moeru no ga...Suki Kai" by Iwasaki Taku. This mode is a reference to Mako's Two-Star Goku Uniform from the anime Kill la Kill. You are able to press 'D' to disable the copyrighted music.
 * "H" key to activate "Hateful Mode". The mode cannot be deactivated until you reset the game. It's is a reference to the game Hatred. Yandere-chan's uniform will turn into a blackish-gray, and the atmosphere will turn red. As with Slenderman mode, this will set the sanity level to minimum. Metal music plays the whole time in this mode. As such, if you encounter Senpai in this mode, it will result in a Heartbroken screen or an Expelled screen if you encounter a teacher in this mode. You are able to press 'D' to disable the copyrighted music.
 * "S" key to activate "Spooky Mode". This mode turns all female students and teachers into skeletons and plays the song "Spooky, Scary Skeletons" by Andrew Gold in the background. While the female students and teachers are skeletons, their bangs seem to disappear. The reason the male students are not skeletons could be that the player would not be able to tell them apart. The Nurse and Osana Najimi do not turn into skeletons. You are able to press 'D' to disable the copyrighted music.

Phantom Girl
If you take a picture in the bathroom on the 3rd floor, a semi-transparent girl about half the size of an average student model will appear in the picture. No matter where Yandere-chan is the ghost will be looking in her direction.

This character used to be behind the single cherry blossom tree behind the school. If you ran into her, your uniform changed into red and black. The outfit change was later removed because many people claimed it was a bug. She was moved to the bathroom because that's where she was killed and the place she originally was was just for testing purposes.

YandereDev says if people wish to have the uniform back, then you must customize the uniform texture yourself.

Starting screen
After about 10 seconds, the screen title will show the darker side of the game for a short amount of time, this including a dark atmosphere, a bloody uniform, and squirming corpses. Pressing the space bar can manually change to the "insane" title screen, but only for a short amount of time as well.

You can make the "insane" title screen last longer by repeatedly tapping the space bar.

If you press F1, F2, F3, F4, or F5, you can change your uniform on the main menu screen.

In an older version, the starting screen had different animations every ten seconds such as Yandere-chan stabbing a student rapidly, being covered in blood while carrying a severed head, and staring blankly at the viewer. The only music played during these scenes are static.

April Fools
For April Fools 2015 YandereDev released Super Yandere 64 and Kuudere Simulator.

Super Yandere 64
This game is a Super Mario 64 remake in Unity with Yandere-chan instead of Mario.

Kuudere Simulator
Kuudere Simulator is the opposite of Yandere Simulator. The main character doesn't want a Senpai and sits on a chair inside of a room. There is also an option that lets players activate a Tsundere Mode, which causes Kuudere-chan to switch to her alter ego, Tsundere-chan. If done right, she'll say the word "Baka" at the push of a button.



Easter Egg Students
Pippi Osu, Midori Gurin and Ryuto Ippongo themselves are Easter Eggs. Pippi is from a game called Osu!, Midori is based on the character Churuya-san from The Melancholy of Haruhi Suzumiya, and Ryuto is the original mascot from the game Osu before becoming a parody character.

Bugs

 * Titan students run into walls, get stuck, and usually move backwards.
 * When a Titan is killed through whatever means, the ragdoll base collapses in on itself, and the body turns into a ball of flesh and rolls all over the place. YandereDev has stated that the bug is too humorous to fix.
 * Some decoration Easter Eggs obstruct the camera view. Ex. Bancho Mode
 * If you are pinned down by a teacher in Cirno Mode, your hair will not show.

Trivia

 * There may be an Easter Egg that one NPC is secretly a magical girl, and there would be an opportunity to see her transform. It's a low priority though.
 * You used to be able to press 'C' to disable copyrighted music. With Cirno Mode now available, it has been shifted to 'D'.
 * YandereDev's favorite Easter Egg is 'Punished Mode'.
 * There used to be a bug that was patched where if you went into Hatred Mode and changed in the Shower Room, your entire body would warp into a terrifying inhuman figure. This was later fixed.SWEETJESUS.png
 * Many current easter eggs contain copyrighted music. Eventually all copyright music in Yandere Simulator will have to be replaced with composed original sound alike music. If nobody volunteers to compose replacement music or if there is no budget to do so, then the Easter Eggs would have to be removed from the game entirely. If people still want the Easter Eggs, then YandereDev said he would keep the silly costumes in the game but no music at all.
 * There may be a Sonic easter egg where Yandere-chan is naked, covered in blue body paint, and moves at 10x speed.