Piranha Plant the newest fighter in Super Smash Bros. Ultimate after the potted character was added as DLC, but players who don't yet have the fighter only have a short time left to redeem their codes and add Piranha Plant to their rosters.
To get Piranha Plant, Super Smash Bros. Ultimate players must register their game before the end of January 31st. The cutoff is officially on Thursday at 11:59 p.m. PT for anyone who wants to wait until the last minute, but the sooner players take the necessary steps, the sooner they'll have Piranha Plant.
If Ultimate players bought their game digitally before January 31st, they've already had their copies registered automatically and should've received a code in their email inbox associated with the Nintendo account. The subject line of that email should read "Thanks for your purchase of the Super Smash Bros. Ultimate game" and might be stuck in a certain folder depending on what email service is used. Redeeming that 16-digit code in the Nintendo eShop will grant players access to Piranha Plant, though it can take up to 10 days for the code to actually arrive in players' inboxes after purchasing the game.
For anyone who bought the physical version of Super Smash Bros. Ultimate, the process is mostly the same, but there's one additional step needed to receive a code. Physical buyers will need to redeem their My Nintendo Points by highlighting the game's icon on the Switch's menu, navigating to its options, and selecting the "My Nintendo Rewards Program" choice to then select "Earn Points." Once that step has been completed, the process proceeds the same as with the digital version with a code being emailed to players' inboxes within 10 business days.
Once that code is received and redeemed in Nintendo's eShop, Piranha Plant will automatically be unlocked, assuming players have updated their game to Version 2.0.0 which is the latest release. If you've already got that code in your inbox, you don't have to redeem it right away since the code won't expire until June 30th. Several DLC characters will likely be out by that time though, so it'd make more sense to redeem Piranha Plant sooner to get used to it before the next release.
Anyone who doesn't register their copy of Super Smash Bros. Ultimate and before the deadline will be able to purchase Piranha Plant at a later date which has not yet been revealed.
Super Smash Bros. Ultimate's update that added Piranha Plant is now live and also included a detailed set of patch notes regarding what's new.