So does helmet guy not have a head? Was he the person whose head got blown off? I can’t ...

Wasn't the flashback the mask dude's though

I’m not sure. When helmet guy touched him, it seemed like he could hear helmet guy’s thoughts, so I’m more inclined to believe that memory was helmet guy’s. Also in the new cover art it looks like black smoke/shadowy under his helmet

Hmm now that you said it it does seem so. Hmm let's see how it is.