Hi again, long time i dont post!

Im trying to make some rock formation for a game, is a mobile game so it need to be low poly.

Now im trying to merge/combine/retopology the mesh i created using copy stamp node. I dont need the inside polygons and vertices so my idea is to make one mesh.
One hack is export this to fbx and in Maya do the retopology by hand.

Is there any node for this issue?

I dont have multiple meshs, is one box that is copy stamp in a grid with random values.

You could try a VDB from poly (SDF) -> convert VDB to poly -> poly reduce.

Yep exactly! That's what I had in mind. Also you can put down a boolean node and set it to union so it unions with itself. But yeah VDB's are great for this.