Puyo Puyo Demo is currentrly available on the Japanese eShop and is a great demo, it includes multiple game modes, local multiplayer, multiple characters and its HD Rumble compatible.It's pretty easy to download, just follow this instructions below:
1. Create a new Nintendo Account using this link: https://accounts.nintendo.com/
2. Make sure you set your country as Japan
3. On your Switch console, create a new profile and link it to your new Nintendo Account
4. Go to eShop on your Switch and select your new account
5. Find Puyo Puyo Tetris and on the right you'll see two boxes outlined in red
6. Choose the lower one which is slightly smaller; that's the demo
7) Hit 'A' and you'll start the download The game is great fun and there is plenty to do in the demo. Enjoy!