The Fire Mage is quite a fun, magicka-based build which attempts to maximise damage output whilst providing methods for survivability in a tight spot.
Good spell damage and penetration combined with AoE, ensures effective annihilation of large mobs but the build is not so great against high damage boss attacks.

Starting by triggering Molten Armaments on skill bar 2, fire off a +40% damage heavy attack to wake up the enemy. It's loads of fun to then dive into a mob, trigger Flames of Oblivion and Volatile Armour before rotating to skill bar 1. By this point there's probably a few new dents added to the old armour. For ground-based mobs put the Burning Talons to use followed immediately by Deep Breath. This will root most enemies to the ground and stun any casters whilst replenishing most, if not all of your health. It also offers a chance to target a more powerful enemy and place Structured Entropy upon it, giving you a slow but regular supply of health and increasing your spell damage by a further 20%.

After this, spam Elemental Ring a couple of times and take another Deep Breath. Most of the mob "should" be down by now, leaving only the big brother of the mob or the stragglers. They usually finished with Engulfing Flames, Molten Whip and a quick medium/heavy attack. Job done (in most cases).