For downloading the game:
Sentinels of the Multiverse’s game definition is hosted on OCTGN’s Game Directory, which you can add as a new Game Feed in OCTGN. In the Games Manager tab of your OCTGN window, click ‘Add Feed’ and paste the following URL: https://www.myget.org/f/octgngamedirectory
For downloading images:
Once you’ve downloaded a Card Package, you’ll be able to add it to your game through the Games Manager tab in your OCTGN window. Push “Add Image Packs,” find your downloaded Card Package, double-click and it should be added to your game. Don’t worry if it takes a while.
Here are the Card Packages currently available for Sentinels of the Multiverse: