Question about Spell Gems

Automaticly cast Spell Gems do not use up Mana, so why do they show Mana cost then? Is there some hidden mechanic or advantage/disadvantage behind this? :thinking:

Another questions: Are Barrier % based damage type effects affected by enemy defense or does it behave like Health % based damage type effects?

If I give Sacrifice to the Light to a Ashmouth Cerberus, it shares that Spell with all my Creatures but if any of them die would be the Original Sacrifice to the light Spell also be destroyed?

Is it a good idea to make a Spell Gem that cost Health instead of Mana and at the same time also has “Potency is based of Health”? Is the Damage calculated before or after the Health got substracted?

I figured it on myself and the answere is it does not get permanently destroyed, works even with supercharged spell gems. Ashmouth Cerberus might be my new favourite Creature.