I never wrote that Ekans had to fight an Entei, just a wild pokemon
''If'' you are defeated by this wild pokemon, you will re-spawn at the last pokecenter you visited. As it is in the guide, you do not have to heal, just walk in and then out. This will help you to save time. For example, If you last visited Bluegum's Pokecenter and your Ekans is defeated, you will re-spawn there.
Changes: I did remove ''Entei'' that was mentioned on the ''NOTE'', that means that there is not spoil.