Why some skills are missing?

Hi, thank you for your question. Mediena's black mage abilities are divided into two groups: main command and sub command.

Blizzard and Bio are main command and icons of them on the ability board are decorated.

Blizzara, Osmose, and Drain are black mage sub command. Once you set Green Mage as sub command, you can't use Black Mage sub command abilities.