How to use a 2d sprite in a 3d game?

So basically, I just want to have a 2d health bar appear over the enemies head, so it is always facing the player, but I have no idea how to implement a sprite into a game other than with GUI.

I just need it to billboard, much like unity’s terrain editor does with trees, and how the grass works

Any ideas on how to do this?

If you already know how to use GUI to make a health bar, why not just use GUI? It would take a bit of translation and math to place it over the character. And it will exist fixed size in front of everything else.

Here is a bit of code that places a texture over the top of a character to demonstrate how to get a GUI to track a game object:

#pragma strict

var toTrack : Transform;
var tex : Texture;
var above : float = 0.95;  // How much offset from center of toTrack;
private var rect : Rect;

function Start () {
	rect.width = tex.width;
	rect.height = tex.height;
}

function OnGUI() {
	var v3Pos = toTrack.position;
	v3Pos.y += above;
	v3Pos = Camera.main.WorldToScreenPoint(v3Pos);
	v3Pos.y = Screen.height - v3Pos.y;  // Convert screen to GUI
	
	rect.x = v3Pos.x - tex.width / 2.0;  // Offset to anchor in the middle
	rect.y = v3Pos.y - tex.height / 2.0;
	
	GUI.DrawTexture(rect, tex);
}