Nintendo has just released update 2.0.0 for Super Smash Bros. Ultimate and it adds Piranha Plant to the game as a playable character among other changes.
So of course if you bought the game and registered it with My Nintendo either already or by January 31st you were/will be sent a code to redeem for the Piranha Plant character. It will also be sold separately at a later date. You can read the full patch notes below
・You can now play Spirit Board with up to four players.
Select the Spirit you want to challenge on the Spirit Board, and then go to Party → Fighter to select the number of people who will play. When playing with multiple people, you will lose the battle if any player is KO’d.
・The below Spirits will now appear in the Shop.
・Golden Dash Mushroom
・Adjusted the calculation method for Global Smash Power.
*Online play requires a Nintendo Switch Online membership.
・Added the DLC fighter Piranha Plant.
*Piranha Plant will become available for purchase as DLC at a later date.
・Pressing both jump buttons at the same time will now cause you to Short Hop.
・Fixed the issue where the KO score included your teammates’ KOs when Team Attack was On.
・Game-balance adjustments. You can see which fighters had specific adjustments on the official website.
・Various gameplay fixes.