HELP- Complex question about layers regarding pixel art:

You can try this:

// split layer;

// 2019, use it at your own risk;

#target photoshop

if (app.documents.length > 0) {

var myDocument = app.activeDocument;

var myResolution = myDocument.resolution;

myDocument.resizeImage(undefined, undefined, 72, ResampleMethod.NONE);

var theLayer = myDocument.activeLayer;

var layerID = getLayerId(theLayer);

var originalRulerUnits = app.preferences.rulerUnits;

app.preferences.rulerUnits = Units.PIXELS;

var docWidth = myDocument.width;

var docHeight = myDocument.height;

// the dimensions;

var theWidth = 8;

var theHeight = 8;

// create array;;

var theVer = new Array;

var theHor = new Array;

for (var m = 0; m < Math.ceil (docWidth/theWidth) + 1; m++) {

  theVer.push(theWidth*m)

  };

for (var n = 0; n < Math.ceil (docHeight/theHeight) + 1; n++) {

  theHor.push(theHeight*n)

  };

// create selections;

var theCount = 1;

for (var y = 0; y < theHor.length - 1; y++) {

  var Y1 = theHor;

  var Y2 = theHor[y+1];

  for (var x = 0; x < theVer.length - 1; x++) {

  try {

  var X1 = theVer;

  var X2 = theVer[x+1];

$.writeln(Y1+"_"+X1+"_"+Y2+"_"+X2+"___"+theCount++)

  rectangularSelection([Y1, X1, Y2, X2], false);

// layer via copy;

  var id14 = charIDToTypeID( "CpTL" );

  executeAction( id14, undefined, DialogModes.NO );

  } catch (e) {};

// reselct layer;

  myDocument.activeLayer = theLayer;

  };

  };

// reset the ruler units;

myDocument.resizeImage(undefined, undefined, myResolution, ResampleMethod.NONE);

app.preferences.rulerUnits = originalRulerUnits

};

////////////////// the functions //////////////////

////// rectangular selection //////

function rectangularSelection (theBounds, add) {

// =======================================================

if (add == false ||  add == undefined) {var idsetd = charIDToTypeID( "setd" )}

else {var idsetd = charIDToTypeID( "AddT" )};

    var desc55 = new ActionDescriptor();

    var idnull = charIDToTypeID( "null" );

        var ref11 = new ActionReference();

        var idChnl = charIDToTypeID( "Chnl" );

        var idfsel = charIDToTypeID( "fsel" );

        ref11.putProperty( idChnl, idfsel );

    desc55.putReference( idnull, ref11 );

    var idT = charIDToTypeID( "T   " );

        var desc56 = new ActionDescriptor();

        var idTop = charIDToTypeID( "Top " );

        var idRlt = charIDToTypeID( "#Rlt" );

        desc56.putUnitDouble( idTop, idRlt, theBounds[0] );

        var idLeft = charIDToTypeID( "Left" );

        var idRlt = charIDToTypeID( "#Rlt" );

        desc56.putUnitDouble( idLeft, idRlt, theBounds[1] );

        var idBtom = charIDToTypeID( "Btom" );

        var idRlt = charIDToTypeID( "#Rlt" );

        desc56.putUnitDouble( idBtom, idRlt, theBounds[2] );

        var idRght = charIDToTypeID( "Rght" );

        var idRlt = charIDToTypeID( "#Rlt" );

        desc56.putUnitDouble( idRght, idRlt, theBounds[3] );

    var idRctn = charIDToTypeID( "Rctn" );

    desc55.putObject( idT, idRctn, desc56 );

executeAction( idsetd, desc55, DialogModes.NO );

};

// by mike hale, via paul riggott;

function getLayerId(theLayer){

// http://forums.adobe.com/message/1944754#1944754

app.activeDocument.activeLayer = theLayer;

//Assumes activeDocument and activeLayer

    var ref = new ActionReference();

    ref.putEnumerated(charIDToTypeID("Lyr "), charIDToTypeID("Ordn"), charIDToTypeID("Trgt"));

    d = executeActionGet(ref);

return d.getInteger(charIDToTypeID('LyrI'));

};