It looks like this in the PEQ Editor. Highly recommend that tool for specific tasks like this one that link multiple tables together.
https://i.gyazo.com/6034ad68498d9021...7fe6ed1e55.png
In this example approximately 1 in 20 kills will result in a squire card of some sort dropping with each card having an equal chance to drop. If you wanted Red to be more rare than the others you'd just make its "chance" lower than all of the others, significantly lower would make it significantly less likely than the others to drop once the drop gets a "hit".