ArchmageG 20

This achievements requires you to equip AND cast all 15 possible spell combinations.
There are 6 spells to unlock through the Road to Rule: Fireball, Shock, Ice Storm, Vortex, Force Push and Blades. All but the Fireball spell cost 40 Guild Seals. Additionally you will need to unlock the Spell Weaving chest that costs 50 Guild Seals for this achievement.

Fireball is always the first chest that has to be opened (during the Castle escape) and costs 1 Guild Seal.
Shock is unlocked after obtaining the Music Box (in the dungeon of the Brightwall Academy).
Ice Storm is unlocked after making promises to both Samuel (Academy reopening promise) and Sabine (Mistpeak restoration promise).
Vortex and the Spell Weaving are unlocked after defeating all of the Hobbes in the coloseum-like area of The Hole (the Mistpeak Monorail quest).
Force Push is unlocked after meeting Page in the Bowerstone Resistance quest
The last spell, Blades, is unlocked after promising Kalin to make Aurora a part of Albion.

These are the combinations possible:
Fireball & Vortex
Fireball & Shock
Fireball & Ice
Fireball & Force Push
Fireball & Blades
Vortex & Shock
Vortex & Blades
Vortex & Ice
Vortex & Force Push
Ice & Shock
Ice & Blades
Ice & Force Push
Blades & Shock
Force Push & Shock
Force Push & Blades