Ironic that I'm writing about Petey Piranha appearing in Smash Ultimate. I hate the name Petey. Anyway, post-launch, Smash Ultimate will be receiving a free new fighter in the form of a Piranha Plant from Super Mario Bros. His final smash will turn him into Petey Piranha (based off of the Mario Galaxy boss).
Piranha will also be getting an amiibo figure alongside the Ice Climbers and King K. Rool on February 15, 2019. That should be fun for fans of the spiky little bastard. The free offer will be for a limited time once Piranha is released, so make sure to nab him up ASAP.
You can find all the details here.