| TEND is an Augmentation symbiosis. If the base spell you're casting (ES in this case) is an Augmentation spell too (which it's not), the only thing that happens is the difficulty increase. If the spell is a Warding or Utility spell, the cast becomes a Hybrid Spell, which means it trains both skills (at a lower rate), uses the lowest of the two skills to determine your effectiveness, and any other features of Hybrid Spells.|
Once we've got the whole list compiled, I'll post it. We plan to have Augmentation and Warding symbioses - Utility symbioses are harder to create while maintaining the continuity of the Symbiosis system, and probably make the most sense for use with a subset of spells. For instance, a Utility symbiosis that augments fire damage of a TM spell might make sense as a WM-only symbiosis. That's just a random idea, not a commitment though.