Shadow Energy is a special type of Hero's resource that can be used in Shadow Era.
In the official Shadow Era's wiki, the term "Shadow Energy" is abbreviated as "SE" (not to be confused with the abbreviation for the name of the game itself).

• 1 Shadow Energy point is gained by your hero at the start of each of your turns (with the exception of your first turn if you go first).
  
• Heroes may gain more than 1 SE point each turn by playing abilities with that special meaning.
• It is appearing as a number within a light purple circle in the lower left corner of your hero card.
  
• Heroes can gain up to a maximum of 10 SE. All SE gained points after reaching 10 are lost.
  

• When the amount of SE your hero has is at least equal to the number indicated in the hero's card type area, your hero can use that ability if valid.
  
• Certain cards other than heroes also have abilities activated by using SE, which will be used from your hero when said ability is activated.
  
• Currently, there is no ability that cost more than 5 SE.