Singletons, Enums and anonymous inner classes

Question

As you may know, some people are declaring singletons with an Enum of 1 instance, because the JVM guarantees that there will always be a single instance with no concurrency

Answer 1

Thus what about an Enum with multiple instances?

There is no such thing, and your example doesn't demonstrate it. You have an Enum with multiple values. They are all singletons.