Legendary Pokemon are being handed out throughout most of this year, and you can get the latest two to be added to the long list next month. March brings the Legendaries Heatran and Regigigas to eager trainers in Pokemon Ultra Sun and Moon or Pokemon Sun and Moon. You can see both powerful Pokemon in action in the new trailer from The Pokemon Company below.
Regigigas is a Normal-type Pokémon, though Heatran is a Fire and Steel-type. You can probably do a fair amount of damage to enemy trainers' teams with one or both of them, but unfortunately without multiple copies of Pokemon games, you'll be relegated to choosing one as your free Pokemon.
To be eligible for the code, you'll have to sign up for the free Pokemon Trainer Club newsletter, which you'll have to do by visiting the official Pokemon site. Your unique code will be mailed to you in March, but you need to sign up for the newsletter to be delivered ahead of March 1 to ensure the code reaches you.
Once you get the code, you can redeem it via the Mystery Gift option to get the Pokemon of your choice. You'll need to enter the code and then visit any Pokemon Center in the game to pick up the new addition to your collection from the delivery man who'll be waiting for you. Then your new Pokemon is ready to stay with you forever.
Be on the lookout for more Legendary Pokemon to come down the pipeline as the year wears on, because there are several more that will be sent out to loyal trainers.