A cool big set!
This set of portrait post cards comes from the big bonus pack that came with Team Sonic Racing game in 2019. Each colorful card features a racer character standing beside their custom car. They also have their name/color on the ground under them. The art is all CG, right from the games, and the character is posed differently for each.
It's a great set, perfect to collect or display. (Maybe in a frame on the wall?)
You can get Eggman, Zavok, Sonic, Tails, Knuckles, Shadow, Rouge, E Omega, Amy, the chao team in their car, Big, Blaze, Silver, Vector & Metal Sonic. (Interesting car choice for Metal Sonic, he copies Sonic's car too, but it looks a little different)

In the gallary is the back of the post cards, they all look the same on the back. It's plain blue (for writing) and has the Game's logo & indicator of where to put the stamp. It' unlikely that any of these are actually meant to be sent, they're more like a large size collector card set. It's a perfect thing to offer as a bonus pack with the game, colorful, easy to collect & display & pleases everyone by featuring every character and car with quality art.

TODO = all sonic postcards seperate in gallary