Certain traits (such as glowing flesh, or bony spines) require the use of Energy Slots/Spheres (ES) to manifest. ES is the total amount of excess energy a Vido can afford to spend to maintain its form outside of essential functions.
As a designer, you can freely choose how this ES is used. The amount of ES on a Vido's masterlist is its total -- meaning that all its traits added together must not exceed that number!
For example, a vido with 5 ES could have Webbing (1), Translucent Skin (2), and Glow (2), totaling to 5 ES. If it is dissatisfied with webbing, it could later change it to Vapor (1), and still total to 5.
Leech Traits are trait modifiers that subtract ES from a Vido's total when added, leeching off of its energy.
A Vido does not have to use all the ES it has available, choosing to reserve it instead. Some traits cannot be added through ES alone, and require a stronger power.