Kirby's Avalanche

Puyo Puyo, but with Kirby characters! ...this is a pretty bad game in my opinion.

This is the first time Kirby can been seen talking. In full sentences too, no less!
Kirby's Avalanche was one of several titles compatible with XBAND, an online service for the SNES that functioned through an expansion cartridge connected to a modem. This technically makes it the first Kirby game with online multiplayer, though the first one with native online compatibility was Kirby Battle Royale, released 22 years later.
The staff credits can be viewed immediately if the game is started or rebooted while player 1 holds L + right and player 2 holds R + left (You're better off doing this or not playing at all).
Interestingly, the modern designs for several characters (such as Kracko and Meta Knight) first debuted in this game, ahead of their appearance in Kirby Super Star. It is likely that this game's development overlapped with Kirby Super Star, so the newer designs were used while the later game was still being developed.
Kirby's Avalanche is one of several international rebrandings of the Puyo Puyo series for western audiences, with other examples including Dr. Robotnik's Mean Bean Machine and the "Bug Drop" minigame in Timon & Pumbaa's Jungle Games.

Although most traces of Super Puyo Puyo were removed from Kirby's Avalanche, the columns in the title screen still have inscriptions that read "PUYOPYO".

All the bosses from Kirby's Dream Land and Kirby's Adventure return as opponents, with the exception of Kabula (who doesn't appear at all because no one likes her or something) and Nightmare (who has a small cameo).
This game, along with Kirby's Toy Box and Kirby Slide (both aren't available here), are the only officially released Kirby games to have never been referenced in games that came out later, the lone exception being the Kirby's History timeline in the North American version of Kirby's Dream Collection Special Edition, where it replaces Kirby's Star Stacker for the Super Famicom, which only released in Japan at the time of Kirby's Dream Collection Special Edition's release.
This is the first game in the Kirby series where the Kirby Dance isn't shown after beating a level/boss

This is also the first Kirby game to have voices, although the announcer is the only one who has voice acting.
This is also the first Kirby game in which King Dedede and Meta Knight are shown to speak.
This is also the first Kirby game to call Meta Knight by his actual name in-game, and the first time his name is revealed internationally.

On the box art, King Dedede is not wearing his gloves. In-game, however, he does wear them.
Despite not being released in Japan, Masahiro Sakurai supervised Kirby's Avalanche. Ironically, Sakurai claims to be really bad at falling-block puzzle games, especially true of Puyo Puyo, of which this game is based.
Squishy's dialogue box wasn't widened for the Ghost Trap name in the European version, so when he speaks the line "An eight-armed Ghost Trap for you then, Kirby!" the word "you" overflows the text box.
During King Dedede's stage, the panic music will never play if the player is close to losing.