Hey myles, welcome! These have been covered a few times here, so if you aren't concerned with spoilers, you should check out the
Berserk Mythbusters post, our version of a FAQ (it even has a podcast version). Here's the part that pertains to the boy in the moonlight:
11. Whaaaat's the deaaaal with the boy in the moonlight?
The boy's identity has not been officially confirmed by the manga yet, but clever readers can put together a pretty solid thesis. He is Guts and Casca's son, appearing to rescue his parents from terrifying scenarios on full moons. He was born as a "demon child" but after being incorporated into the Incarnation Ceremony as the "flesh" of Femto's incarnation, the boy can apparently manifest on full moons, which "makes minds more unhinged" and during which magic is more effective. We saw on the Hill of Swords that the boy can influence Griffith's actions. He forced him to rescue Casca from falling boulders (just like he rescued Casca any number of times previously). And on full moons, he can apparently appear as his own self and visit his parents.
Most of your questions are answered here, but to briefly address each:
i'm on my second read of berserk and i still don't understand how it works so if anyone is willing to answer my questions that would be dope.
also this might be redundant if theres another thread about the same thing but pls bare with me on this one
1.if you kill Griffith does the kid die
2.if so does it go vice versa
3.here has he been the whole time
4.is he an astral being
5.what's the explanation for when he turns into the deformed blob thang
6.is it guts' kid or nah
1. Unknown, but yes it would make sense.
2. Sure?
3. Not sure what you mean. He's been around since just after the eclipse. He appears at night (like specters), and after the incarnation ceremony his body is used by Femto to incarnate. When you see Griffith now, that's the boy's flesh being subverted by Femto.
4. Not known. The boy is a unique being who doesn't fit neatly into the definitions for these things we usually use.
5. That was the fetal form of the boy, which we will likely never see again.
6. Yes, he is Guts and Casca's child, tainted by Femto and ultimately used by Femto as a vessel for his astral body.