I am trying to create a Rust mod to send custom environment updates. I have tried to extend the EnvSync class and override the Save function with my own but it is not working as I expected. Is it possible to override an entity's function with my own in Rust? Or delete the original entity and create a new one with my modified class?

If you make a new class and have it inherit from MonoBehaviour, then attach it to entities as a component, you can sort of do something like that.  I've done that to add code to the FixedUpdate() method on some entities.

What you want to do sounds a little more involved; I'm not sure how to pull that off.  But there are some pretty smart guys on here so maybe someone has the answer for you.

Maybe I'm on the right track then. Do you have an example of how you added code to FixedUpdate()?

This is what I am attempting to do right now.

EnvSyncOverride _envOverride = _envSync.gameObject.AddComponent<EnvSyncOverride>()

public class EnvSyncOverride : EnvSync
{
    public override void Save(SaveInfo info)
    {
        base.Save(info);
        // custom code
    }
}​

Mine's sort of like that.

public class ZugController : MonoBehaviour
{
	// vars and methods and stuff
	
	public void FixedUpdate()
	{
		// more stuff
		// this code runs in addition to whatever happens in the entity's original FixedUpdate
	}
}​

I think whatever methods you are trying to add to, have to be 'virtual' or 'override'.