If you’ve purchased a physical copy of Super Smash Bros. Ultimate, you’d probably want to register your game on My Nintendo as soon as possible.
My Nintendo members who register their game on My Nintendo by January 31, 2019 will receive a code to redeem Piranha Plant as a fighter for free later this year. To register the game, head over to the Home Menu, place your cursor over Super Smash Bros. Ultimate, press + (plus), go to “My Nintendo Points Program”, and then select “receive points”.
If you purchase the game digitally by January 31, you’ll automatically receive a code on the email address of your My Nintendo account within 10 days of purchase.