Hi, seforums!

Started to make a mod, but do not know how to change the main menu.

Created 3 class.

One mistake.

How to fix?
Added in the main class:

	  @EventHandler
	  public void preInit(FMLPreInitializationEvent event) {
		  MinecraftForge.EVENT_BUS.register(new RPGMainMenuEvent());

Added in the RPGMainMenuEvent class : (There is just a mistake!)

package ru.Morttal.RPGcore.gui;

import net.minecraft.client.gui.GuiMainMenu;
import net.minecraftforge.client.event.GuiOpenEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;

public class RPGMainMenuEvent {
	 @SubscribeEvent
	    public void onGuiOpenEvent(GuiOpenEvent event)
	   {
	     if ((event.gui instanceof GuiMainMenu))
	     {
	      event.gui = new RPGMainMenu();
	     }
	   }

	}

Added in the RPGMainMenu class: 

package ru.Morttal.RPGcore.gui;

import net.minecraftforge.fml.relauncher.SideOnly;

import org.lwjgl.opengl.GL11;

import net.minecraft.client.gui.GuiButton;
import net.minecraft.client.gui.GuiLabel;
import net.minecraft.client.gui.GuiMainMenu;
import net.minecraft.client.resources.I18n;
import net.minecraft.util.ResourceLocation;
import net.minecraftforge.fml.relauncher.Side;

@SideOnly(Side.CLIENT)
public class RPGMainMenu extends GuiMainMenu {

    private static final ResourceLocation texture = new ResourceLocation("textures/gui/achievement/achievement_icons.png");

    public RPGMainMenu() {
        super();
    }

    @Override
    public void initGui() {
        int i = this.height / 4 + 48;
        this.buttonList.clear();
        this.buttonList.add(new GuiButton(0, this.width / 2 - 100, i + 72 + 12, 98, 20, I18n.format("menu.options", new Object[0])));
        this.buttonList.add(new GuiButton(4, this.width / 2 + 2, i + 72 + 12, 98, 20, I18n.format("menu.quit", new Object[0])));
    }

    @Override
    public void drawScreen(int mouseX, int mouseY, float partialTicks) {
        GL11.glColor4f(1, 1, 1, 1);
        drawDefaultBackground();
        mc.renderEngine.bindTexture(texture);
        drawTexturedModalRect(0, 0, 0, 0, mc.displayWidth, mc.displayHeight);
        //---

        for (int i = 0; i < this.buttonList.size(); ++i)
            ((GuiButton)this.buttonList.get(i)).drawButton(this.mc, mouseX, mouseY, partialTicks);

        for (int j = 0; j < this.labelList.size(); ++j)
            ((GuiLabel)this.labelList.get(j)).drawLabel(this.mc, mouseX, mouseY);

    }

}

How to fix error is in 2 class? not working event.gui

BTW there is already a mod for changing the menu through a json config file. Its called CustomMainMenu and there's a version for 1.12.2