From the author's README on Thunderstore

Element x MLB For Life Series Remake Pack

A massive collection of board graphics based on Element's MLB Collaboration remade from scratch. All 30 Baseball team decks and one alternate (Guardians)

Side Note: Half of the designs I couldn't find the originals for to use for reference, I tried my best to make similar ones but they aren't perfect.

Install Element x MLB Pack

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Element x MLB Pack and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.