What were known as essences or energies – other than mana and its derivatives like Aura and Nitros – were usually mutations that had mana entangled within them; spiced mana, as some referred them to as. When Skullius had reforged his mana core back when Sila destroyed it, he had learned the flow of Distorted Gravity by reading how the mana moved with the influence of it.
Many significant essences could be learned this way, and many couldn't, mostly because they were far removed from mana. In any case, the relationship an expert had with any essence was what was called an affinity. The higher the affinity, the better their understanding, control and production of said essence.
Replicus had more than ten affinities with different kinds of essences, but only used a few that were actually relevant.