How would I make a custom Heart?

everything is possible, but what you want is not possible without coding, and the process is quite complicated.

you're gonna need to hook net.minecraftforge.client.event.RenderGameOverlayEvent event, check if the event element type is ElementType.HEALTH, if so, cancel it, get the screen resolution and start drawing your own hearts.

to start yourself off, you could create an overlay in mcreator, draw the hearts there, save and build it, and then edit that overlay's code. in that code you will find its checking for ElementType.HELMET, change it to HEALTH, cancel the event, then modify the code as needed.

HUH did u say that u can cancel de Health bar?!????, please show me how. i need that, u know, when you make a mod with player that have over 300 HP and need to remove health bar cuz it hide 4/9 of ur screen...

like I said, start yourself off with creating an overlay in mcreator. use "add images" to add little hearts that you made, or just put one image at the start position of your new health bar. save and build the overlay.

next you'll have to edit the overlay's code. find the line: 

if (!event.isCancelable() && event.getType() == RenderGameOverlayEvent.ElementType.HELMET) {

and change it to:

if (event.isCancelable() && event.getType() == RenderGameOverlayEvent.ElementType.HEALTH) {

then somewhere below you'll need to add a line

event.setCanceled(true);

to cancel forge drawing the health bar. 

next you'll need to write your own code to calculate where to draw your new health bar. the start position is already there in the code when you used the "add images" in the mcreator overlay creation gui.

is something like this ok for an overlay(about the Ki bar, dont worry its just some kind of energy)Imgur: The magic of the Internet

It work fine but it makes the Food Bar bugged

yeah, i believe thats because the binded texture is not correct. add a line at the end of the above mentioned if block:

Minecraft.getInstance().getTextureManager().bindTexture(AbstractGui.GUI_ICONS_LOCATION);

don't forget to import AbstractGui

when do i import AbstractGui each time i put it at the beginning, its just make an error

show me your code. also, which version of forge are you modding?

sorry im late. its 1.15.2:

package net.mcreator.dbm.gui.overlay;

import net.minecraftforge.eventbus.api.SubscribeEvent;
import net.minecraftforge.eventbus.api.EventPriority;
import net.minecraftforge.common.MinecraftForge;
import net.minecraftforge.client.event.RenderGameOverlayEvent;
import net.minecraftforge.api.distmarker.OnlyIn;
import net.minecraftforge.api.distmarker.Dist;

import net.minecraft.world.World;
import net.minecraft.entity.player.PlayerEntity;
import net.minecraft.client.Minecraft;

import net.mcreator.dbm.DbmModVariables;
import net.mcreator.dbm.DbmModElements;

@DbmModElements.ModElement.Tag
public class InfoBarOverlay extends DbmModElements.ModElement {
    public InfoBarOverlay(DbmModElements instance) {
        super(instance, 44);
    }

    @Override
    public void initElements() {
        MinecraftForge.EVENT_BUS.register(this);
    }

    @OnlyIn(Dist.CLIENT)
    @SubscribeEvent(priority = EventPriority.NORMAL)
    public void eventHandler(RenderGameOverlayEvent event) {
        if (event.isCancelable() && event.getType() == RenderGameOverlayEvent.ElementType.HEALTH) {
            event.setCanceled(true);
            int posX = (event.getWindow().getScaledWidth()) / 2;
            int posY = (event.getWindow().getScaledHeight()) / 2;
            PlayerEntity entity = Minecraft.getInstance().player;
            World world = entity.world;
            double x = entity.getPosX();
            double y = entity.getPosY();
            double z = entity.getPosZ();
            if (true) {
                Minecraft.getInstance().fontRenderer.drawString("Ki:", posX + -207, posY + -103, -16724737);
                Minecraft.getInstance().fontRenderer.drawString(""
                        + (int) ((entity.getCapability(DbmModVariables.PLAYER_VARIABLES_CAPABILITY, null)
                                .orElse(new DbmModVariables.PlayerVariables())).Ki)
                        + "/" + (int) ((entity.getCapability(DbmModVariables.PLAYER_VARIABLES_CAPABILITY, null)
                                .orElse(new DbmModVariables.PlayerVariables())).KiMax)
                        + " ", posX + -198, posY + -103, -16724737);
                Minecraft.getInstance().fontRenderer.drawString("Health:", posX + -207, posY + -112, -16724890);
                Minecraft.getInstance().fontRenderer.drawString(""
                        + (int) ((entity.getCapability(DbmModVariables.PLAYER_VARIABLES_CAPABILITY, null)
                                .orElse(new DbmModVariables.PlayerVariables())).Health)
                        + "/" + (int) ((entity.getCapability(DbmModVariables.PLAYER_VARIABLES_CAPABILITY, null)
                                .orElse(new DbmModVariables.PlayerVariables())).HealthMax)
                        + "", posX + -180, posY + -112, -16724890);
            }
        }
    }
}
 

?

yeah sorry, if you don't reply to my post i won't get notified.

put this line at top where the imports are:

import net.minecraft.client.gui.AbstractGui;

and then put this line in at the end of that if statement:

if (event.isCancelable() && event.getType() == RenderGameOverlayEvent.ElementType.HEALTH) {

    ...

    Minecraft.getInstance().getTextureManager().bindTexture(AbstractGui.GUI_ICONS_LOCATION);
}

I can't code the armor bar. 

If I had written ALL and I wrote ARMOR instead. So I wrote a mistake.

Here is the code:
if (event.getType () == RenderGameOverlayEvent.ElementType.ARMOR)