Upon starting the game, players will select an egg, which will hatch after a short period of time. After the baby hatches from the egg, the player can choose a name for it. Up to three characters can be raised at one time.
All characters from P1 and P2 are featured, but a P1 character may evolve into a P2 character and vice versa. When the Tamagotchi grows old, or if it was sick for too long without being treated, it may die. If the Tamagotchi was a high age, has won a number of contests, and has lived a well-trained, healthy life once it dies, it will show it happily going back to Tamagotchi Planet in a UFO and then it will appear in a "Tamagotchi Hall of Fame".
The game introduces four new parameters to the check meter - intelligence, body, stress and selfishness. These parameters provide the primary influence towards evolution and most of them reappear on future video games in the vintage era. While intelligence and body show up in similar bars to the discipline meter on default, stress and selfishness can only be seen if the player holds select, down and the A button. Whichever is highest out of intelligence or body determines what adult a teenager evolves into out of a set pair - if both stats are equal, the evolution is random; while stress and selfishness determine the tier of the possible resultant adults. A Tamagotchi will lose a quarter of its intelligence and body points every time it wakes up.
There are three options for meals and two snacks - every Tamagotchi has their favorite and least favorite meal, for example ShiroBabytchi likes bread/rice balls but hates meat. Meals include bread (rice balls on the Japanese version), meat and carrot; while the snacks are ice cream and cake. Feeding a Tamagotchi a snack or its least favorite meal increases stress by four, while feeding it its favorite meal decreases stress by two. The Tamagotchi in the game are notable for having a very low tolerance for snacks - two in a short period of time are enough to make it sick, and not very many more afterwards will kill it.
There are various mini-games, such as "Left or Right" from the original P1. There are also games to increase the Tamagotchi's skills - a math game to raise its IQ where the player must press the directional pad to encourage the Tamagotchi to move toward a certain answer, and a sports game to raise its Body where the Tamagotchi must catch a number of falling baseballs. Raising these parameters is a must as they will liken the chances of the Tamagotchi evolving into a healthier adult and so that it can compete in contests when it is an adult. The contests include a race, a beauty contest, and a math test. Whether the Tamagotchi wins depends on its skill levels.
The game introduced the ability to stick a Tamagotchi onto a potty or the toilet if the toilet icon is selected while it is doing the about-to-poop animation. If they successfully do so, there will be no need to flush the screen afterwards and the player will have the opportunity to praise the Tamagotchi.
The game features two kinds of medicine - an injection and a bottle of medicine. Certain breeds may heal quicker with one kind of medicine than they would with the other.
The game has two forms of discipline that will boost the deeds gauge - the usual scolding, and praising which would be reused in modern releases starting from the Tamagotchi Connection. The player must scold their Tamagotchi when it is throwing a tantrum or refusing to eat or play even if its meters are partially empty, or praise it after winning a math or sports game, going to the toilet instead of pooping on the floor or winning a contest.
There are three kinds of competitions that teenage and adult Tamagotchi can be entered in - races, math tests, and beauty contests. A Tamagotchi can only be entered in a competition once a day, and its performance depends on its stats, parameters and breed.
Races are dependant on a Tamagotchi's body stat, pitting them up against three other Tamagotchi. The player can rapidly press the A button to speed up their Tamagotchi, but pressing it too much will tire it out for several seconds and almost guarantee its loss. A Tamagotchi's speed will gradually increase over the first six times it participates in a race.
Math tests are dependant on a Tamagotchi's intelligence stat, and function similarly to the studying game. There are two rounds, a basic round and an advanced round - while a Tamagotchi with sufficient intelligence will likely clear the basic round, they will likely fail the advanced round on their first attempt. The Tamagotchi will lose the competition when they get any question wrong, and their performance wilk improve on their second performance onwards.
- Oyajitchi secret character; evolves from Masktchi and Zuccitchi
- Bill secret character; evolves from both Oyajitchi and Sekitoritchi
- Sekitoritchi secret character; evolves from Masktchi and Zuccitchi
- Sometimes Maskutchi will mysteriously appear in the window of the room, and later disappear all of a sudden.
- This is the only English game that includes Professor Banzo and Mikachu.
- All the Tamagotchis are in their original Japanese designs, even in the English versions.
- Sprites for Bill's Japanese design are present in the data despite it being the P1 line secret character. These sprites are only in the Japanese version while Bill uses his American design in the international versions. Maskutchi and Zuccitchi can evolve into Oyajitchi in both the Japanese and international releases of the game, and Bill instead evolves from Oyajitchi and Sekitoritchi.