End Portal starfield effect

Create a bunch of textures and then use the "Add Animated Texture" button and compile them into one texture

For the actual starfield effect, you would have to make thousands upon thousands of textures. But another way to do it is to simulate the compass, and have it so that if the player is facing one way, the item would change to a certain texture. I don't know how to do this, but you could probably look for other forum discussions.