Tenebrium is a weapon type and seen in
Seeing as how you have to do so much setup, it isn't exactly an easy invulnerability to reach. But I do agree that comeback kid and leech need a tweak in how they work with each other.
As for the books, if you think it's overpowered, don't use it. If you follow the storyline your main 2 heroes are
some sort of demigods so it would seem appropriate that you get some power boosts not accessible to the regular populace
