PSA: Check your emails if you purchased Smash Ultimate digitally on the eShop.— Pixelbuster (@Nitomatta) November 6, 2018
You'll be able to redeem your code for Piranha Plant, currently lists a release date of Early 2019. pic.twitter.com/BLITSCw76I
Piranha Plant won't be joining Smash Bros. Ultimate until 2019, but Nintendo is already getting things ready for customers who preloaded Smash Bros. Ultimate. Keep an eye on your email for your Piranha Plant code, and make sure to keep it safe for use later!