Magery and Evaluating Intelligence do two different jobs, and people mix them up constantly. Magery governs whether the spell casts at all. Eval Int governs how much damage it does when it lands. A mage with 120 Magery and 100 Eval Int casts reliably and hits softly.
This is the scroll that takes the damage side to its ceiling. It stacks with the Spell Damage Increase on your suit and with Inscription, so it is the foundation the rest of a damage mage is built on rather than a finishing touch.
Legendary powerscroll, cap raised from 100 to 120, one character, consumed on use. Worth pairing with 120 Magery if you are building the character from scratch — the two are only really worth having together.