One of the features of RenPy is that you can use PyGame to build more than just a simple Visual Novel-style game. When you first install RenPy, there is a “tutorial” project you can view, which has a pong game under the demo_minigame.rpy file. You can also find additional information about writing mini-PyGame games in your program in the documentation. For example, the Displayable class docs are useful.
Of course keep in mind, that these are not the final graphics for the game. It’s too easy to get obsessed with trying to create nice graphics that it hinders you from the actual programming, so these are placeholders – no animation, rough drawing, etc. Think of it as a rough draft.
If you’re curious about how I implemented the fish-catching game, everything is Open Source! Check it out on the GitHub project for “Project Doggie”. This sample is under the RenPy > minigame test folder, since I’m working on these separately from the actual game, so things don’t get all cluttery.