Despite having more mana than necessary to cast the spell, the Mage player specialization doesn't allow you to cast Mind Blast at less than 5 mana.

version: 0.5.22b-Win64

Looked into the code of 0.5.23c-Win64, and the issue is much more broad. In "combat.gd", the function "pressskill(skill):" does not consider Mage player specialization for any skill. Probably was never noticed because mana is rather easy to acquire.

While looking into this I found that mindblast and acid spit are both spells and abilities, and the entries don't match. The info listed in the player inspection's Spell Book is from "spells.gd", but combat only uses "abilities.gd" so in these cases(perhaps others) the book is wrong about combat values.

There is an old bug that I'd like to include with this for completeness: the double purchase of spells. This bug is from "Mansion.gd", in "_on_abilitypurchase_pressed():" the spell purchased is never marked as 'learned' and the spell store of "outside.gd" in "mageservices():" offers spells so long as they have not been marked 'learned'. When you purchase 2 copies of a spell/ability, they have identical identification codes. Therefore, the game sometimes treats it simply as though you have the same spell twice. But other times, like the Spell Book, the game only checks if a spell has been marked as 'learned', thus the player doesn't have a spell until it has been purchased from the spell store.