From time to time I see people ask if they can mix pantheons in Paganism. The answer is, “Why not?” There’s really nothing in Paganism that says you can’t mix pantheons. Even if you belong to a coven that strictly follows one pantheon there is nothing, or should be nothing, to prevent you from mixing pantheons in your personal practice.
Most Pagans hold the belief that there is more than one path to the Divine. That our own path is not the only way there. This means that we acknowledge that deities other than our own are valid as well. Basically, all of the gods are real. If all of the gods are real then why should we consider any of them “off limits” to us? There really is no good reason to deny ourselves access to different paths to the Divine.
There are those who theorize that you should only work with a pantheon that is part of your ancestry. While there’s nothing wrong with going that route, if that’s what appeals to you, the question is why should you limit yourself? Explore different pantheons and see what gods and goddesses call to you. Trust your instincts. If you feel a pull in a certain direction follow it. There’s no need to stick to your genetic background if that’s not the path that feels right to you. You may want to follow gods from your ancestral background and gods from other backgrounds as well. It’s perfectly fine.
Do the gods from different pantheons play nicely together? If you are thinking about doing a ritual or spell where you will be working with gods from two different pantheons you may want to do some meditation first where you ask each deity how they feel about working with the other. Chances are there won’t be any problems as long as their energies complement each other. Pagan gods generally don’t have a problem working together, as there isn’t a power struggle between them. Pagan gods don’t get jealous of you working with other Pagan gods. So if you work with Hecate today and the Morrigan tomorrow neither of them is going to hold it against you.
There is no good reason to limit yourself to one pantheon unless that is the path you choose for yourself. Study up on some different pantheons and see what you find. Maybe you’ll be called to work with some of those deities and maybe you won’t but either way the knowledge you get from studying them can only enrich your practice whatever path you choose.