Hello, I couldn’t find this explained anywhere... I am very new to the game and have Synchronicity in my deck. The way I understood the card is that as long as I have at least one dice showing a shield and another showing a melee I can play the card. However my opponent said that my dice can only be showing those symbols (shield and melee). So if I have other dice in the pool showing any other symbol, a Blank for example, I cannot play the card. Which is correct?

You are correct. You can play it any time you have dice showing both symbols, regardless of what your other dice are doing.

I think your bud might be hung up on the "play only" in the text, that is simply a play restriction meaning that you cannot play that card at all without meeting the requirement of having those sides showing. But you are correct

Thanks for the replies!

Sounds like your opponent didn't want to take damage.