I believe in everything, by definition. I define everything as "all of that which is." So of course I'd believe in it!
I don't concern myself with determining what does or doesn't exist. That's its problem. If it does, I believe in it. If it doesn't I don't! That's the sweet peremptory blessing that I lay down: "Hey, all of that which might or might not be, whether you exist or not, that's your problem. If you exist, then I thereby believe in you. If you don't, then sorry: too bad. I refuse to believe in what doesn't exist."
It's good to have an easy rule to go by.