The Freezie is an enemy in the Mario Bros. arcade game (where it was known as a "Slipice") and all of its subsequent remakes. It appears in later levels to complicate the terrain. It moves along the platforms and then eventually covers one of them in ice, destroying itself in the process. This makes the platform extremely slippery for players. If Mario makes contact with a Freezie, he loses a life. The only way to destroy it is to jump into the platform below it, as is the case for combating any enemy in Mario Bros.
In Super Smash Bros. Melee
When a Freezie appears in Melee, it slides across the stage on its own, speeding up if it encounters a slope. When picked up and thrown, any character hit by the Freezie will be frozen and knocked upwards. Freezies can break if attacked before being picked up. Freezies can KO characters at respectable percentages, as well as keeping characters trapped long enough to take considerable damage.
Melee trophy description
In Super Smash Bros. Brawl
The Freezie item in Super Smash Bros. Brawl retains the same design and method of use from its Melee counterpart. However, their knockback and freeze time have been considerably reduced, and frozen characters fall much slower, making it harder to KO with. Freezies are also more difficult to destroy, and they may deal damage after they are destroyed to any player standing near them and can also freeze multiple foes at once. In addition to these changes, sound effects taken from the Mario Bros. arcade game play whenever the item is used or shattered. If broken by a physical attack, the attacker will sustain 2% damage and no knockback (but will flinch, interrupting whatever motion they're engaged in).
Brawl trophy description
In Super Smash Bros. 4
The Freezie returns in Super Smash Bros. 4, retaining its behaviors from Brawl. Instead of sliding off edges, it will turn around and move in the opposite direction, but it will still slide off slopes.
SSB4 trophy description
In Super Smash Bros. Ultimate
As an item, Freezie has been heavily nerfed in Ultimate. It deals considerably less knockback, lacking KO potential even at high percents when smash thrown. However, the changes to the ice effect grant the freeze improved followup potential.
In addition to the above, equipping the Mr. Frosty, Alolan Vulpix or Hockey Players Support Spirits will give the player a Freezie at a start of a match.