[Snake]

But thinking of it now that you said, if that is Tarnada's own power alone... Then why Charge Mind + Tavyl should ever affect it?

It doesn't make sense for an Evoker to empower Tarnada's power, if it doesn't belong to them. It's the same as Charging Mind and touching another Evoker when they are about to cast a magic, to empower the friend's invocation.