Piranha Plant was recently added as the newest playable character in Super Smash Bros. Ultimate. However, using this fighter in the All-Star Mode could corrupt your save file, as explained by Ash Paulsen:
#SmashBrosUltimate PSA: I can’t verify this with 100% certainty, but I’m seeing multiple reports that using Piranha Plant in All-Star Smash can *corrupt your save file*, so just in case BE VERY CAREFUL and maybe avoid taking Piranha Plant into All-Star for now! #NintendoSwitch
Source: Ash Paulsen 🏳️🌈 @AshPaulsen
Pokémon Blog 
Once you have anything beyond “Hey this happened to me” or screen shots of empty rosters. Then it’s news. Right now, it’s just rumors in the wind.
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