A small game component named Pulse. It defines a property OnEnabledDoo (a Doo type with an argument hint for SpriteRenderer) and a SpriteRenderer reference, and overrides OnUpdate but leaves it empty.
using Sandbox;
public sealed class Pulse : Component
{
[Doo.ArgumentHint<SpriteRenderer>( "RedCircle" )]
[Property] public Doo OnEnabledDoo { get; set; }
[Property] public SpriteRenderer PulseRenderer;
protected override void OnUpdate()
{
}
}