From the Super Mario Wiki
Small Piranhas are a variation of Fire Piranha Plants that appear in Super Mario 64 and its remake, Super Mario 64 DS. They attack by quickly sprouting from the ground with a harsh hissing noise, then blasting a small fireball before disappearing. Like with normal Piranha Plants, they can be defeated with a basic attack, which grants a single coin. One appears in Tiny-Huge Island, next to the tiny island's Shrinker Pipe where the five large versions are located on the huge island, and two appear in Bowser in the Sky. Unlike the other Piranha Plants in this game, Small Piranhas do not shrink back into the ground upon defeat, but they instantly disappear instead.
In Super Smash Bros. Ultimate, they are mentioned briefly by Viridi during Palutena's Guidance dialogue for Piranha Plant. Unlike most other variations generally mentioned in order of appearance, they are listed between Mario & Luigi: Superstar Saga and Mario & Luigi: Partners in Time debuts, which would place them at the release of Super Mario 64 DS rather than Super Mario 64. Big Piranhas, Nipper Spores, Big Fire Piranhas, and Fire Stalking Piranhas are similarly listed out of order.
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