Evatchi (Evangelion Nano Tamagotchi)

Functions

After the clock is set, a screen showing the Second Impact will appear for several seconds before the baby Angel hatches from its bakelite container.
There are four growth stages: baby, cocoon, adult, and special.

It will stay as a baby for 24 hours before evolving into a cocoon, and the cocoon will be able to evolve to the adult stage three hours later, when the A button is pressed. If the adult Angel reaches the conditions for a special evolution within 72 hours, it will become a cocoon again and then evolve into a special character; otherwise, it will depart on its own.

There are no on-screen icons, and therefore all information is conveyed through the screen, buttons, and sounds.
If the Angel needs something, you can press the C button for an animation to see what it needs. If the Angel shows a dizzy emote, it's hungry; if it shows a scowling emote, it's unhappy. If both Hungry and Happy meters are partially filled, it will perform a happy animation. If the Happy meter is full and the Hungry meter is not entirely empty, it will perform a Close Up.

Pressing the A button opens the main menu:

• FEEDING
• GAMES

The meal is an S² Engine, and the snack is a watermelon. The meal fills up hunger meter, and the snack (and playing the games) fills up happiness meter. You need to feed it 4 meals to fill up the hunger meter. You need to feed it 4 snacks (or win 4 times when playing a game) to fill up the happiness meter.

Cocoon Stage

After 24 hours, the baby will evolve into a Cocoon. During this time, you will not be able to feed it, play games, or check the status, only switch to the clock and turn the sound on and off. After three hours, the evolution noise will play and the cocoon will stop wiggling. If you press the A button, the cocoon will evolve into its next growth stage. Waiting longer periods of time to evolve it will alter which Angel it becomes. It will become a cocoon a second time if an adult Angel reaches conditions necessary for a special evolution.

Baby (24 hours)

Cocoon (can be hatched after 3+ hours)

Games

There are two games, referred to as "Simulations".

Battle Training

Targeting

LCL Cleaning

Throughout the day, the LCL around the Angel will get dirty. Pressing the A button will clean it. The longer you wait to clean it, the dirtier the LCL will become. You will not be able to feed the Angel or play games with it until the LCL is clean.

A.T. Field

If the Angel is neglected for a long period of time, it will put up an A.T. field around itself. The user can coax it out by pressing the A button. While the Angel has the A.T. field up, you can't feed it or play the games, but you can still check the clock, turn the sound on and off, and check needs with the C button.

Daily Events

Throughout the day, animations of various other characters from the Evangelion franchise will appear. Pressing any button will trigger the animation to end, with some showing an additional screen before closing. The animations will not play during the cocoon stage.

Sleep

When the Angel is asleep, pressing the A button brings up the Lights On / Off menu. In the baby stage it goes to sleep at 8 PM, in the adult stage it goes to sleep at 10 PM, and both stages wake up at 7 AM.

Death and Departure

The Evatchi has two known ending sequences:

If you maintain good care and make enough care mistakes, the Angel will depart on its own and trigger the Third Impact, leaving a black screen with the message

If you neglect the Angel and fail to coax it out of its A.T. field, it will be killed by NERV, leaving an image of a giant cross explosion. The animation differs slightly between each Angel, showing which character from the series killed it just before the explosion.

In both instances, pressing A and C together will trigger a new baby to appear.

* Source: TamaWikia (copied and slightly edited)