The "Puyo Puyo" series is a series of colour-coded Tetris-like 1-on-1 action puzzle games, originally developped by Compile.
In Puyo Puyo, players navigate pairs of coloured blobs (puyos) falling down to the bottom of the screen. The falling blob pairs consist of two blobs of the same or different colours.
As they touch ground, the blobs will fusion with any orthogonally adjacent blobs of the same colour; they do not have to form a single line, as long as they are adjacent. If 4 or more blobs of the same colour melt together, they disappear, and whatever was on top of them falls down to fill the hole. This may cause "chain reactions" as the blobs that fall down now in turn might happen to fuse together with others of the same colour.
The point of Puyo Puyo is to form such chain reactions, as the points increase exponentially for each chain reaction. Also, each time a player gets points, neutral non-coloured "nuisance puyo" drop down on the opponent's screen; the more points the more nuisance puyos. These nuisance puyos would only popped if an adjacent blob popped.
A trademark of Puyo Puyo are the characters that appear in each game. Despite being an abstract puzzle action game, the player chooses a character to play. There is no difference between the characters except the background graphics and vocal shouts when chain reactions are formed.
The protagonist and symbol character for Puyo Puyo is a blue-clad brown-haired girl named Arle Nadja.
In the first iteration of Puyo Puyo, there was no "countering", which roughly meant that the first player to get a five-time chain reaction won, as it was enough to fill the opponent's screen. Even if the opponent got the same kind of chain reaction only a split second later, he would still be the first to get his screen filled.
This was fixed in the second iteration "Puyo Puyo 2", where if both players got points, they would nullify each other. There was a small time lapse in between gaining points and raining nuisance puyos, which allowed a small window for countering.
In "Puyo Puyo SUN", the third iteration, nullifications of this kind energized a sun, which if full would drop one or several sun-shaped blobs on both player's screen. These "sun-puyo" would pop if anything adjacent to them popped, and would multiply the points for that pop by pretty much.
Despite many successful years with Puyo Puyo during the 90s, Compile bankrupted in 2003, at which point the brand was bought by Sega.