I've looked through a few boxes of stuff recently and noticed that I also have a Mattel Baseball handheld.
Can you open it and check out the CPU? The case might have those funky triangle head screws, but I can usually get a small flat blade screwdriver to work.
It does have the triangle screws. I couldn't get any of my screwdrivers to work. I'm visiting my parents in a few days, and I'm sure my dad has a much better screwdriver collection than I do. So I could try that.