my enemy is behind the background layer and is not visible
I am assuming this is a problem and you want the enemy in front of the background layer.
In the Sprite Renderer component on your enemy there will be a drop down menu for Additional Settings. That has access for Sorting Layers and Order in Layer. In the Tilevania project Rick is using sorting layers to determine visibility instead of the order in layer.
You can click on the sorting layers dropdown box and it will show you all of the layers you have made and give you the option to add a sorting layer. You can make an enemy sorting layer and position it with a greater # than the background sorting layer. That way anything you set to Sorting Layer enemy in their sprite renderer component will show up in front of the background (and anything else with a lower # in the sorting layer).
Hope this helps!