Fireball

The Fireball is a magical fire spell, dealing decent direct hit and Area of Effect damage. Aimed using either lock-on or manually, the fireball works best from close to medium range. Fireballs can also be charged by holding right click, exploding for extra damage. This offhand also makes use of Critical; casting while you have maximum Critical deals even more damage, and a fully charged critical fireball has a parry break. Any fireballs that aren't fully charged crits can be parried.

Guide
Using this offhand mid-combat isn't very hard. Be careful, because the somewhat slow startup leaves you a little open. Charging the fireball isn't as viable, however. Try charging anytime there's an opponent incoming who's already far away. Crit fireballs are very strong, though. Even without any charging, just tapping right click with full Critical can do almost instant 15%-25% damage.