Build:Archmage

Full Build Details
'''NOTE: This is an endgame build, one of the most powerful mage build. Multiple playthroughs and the use of Legacy Chests are needed to obtain some of the equipment.'''

The idea of this build is to utilize the "stacking effect" of Sigils (i.e. if you place multiple Sigils on top of each other, casting certain spells while standing within all Sigils will interact with all of them at the same time.) to deal massive elemental damage with each hit. Unlike other mage builds, this build does not require a lot of mana. Therefore, the equipment is chosen in a way to maximize fire, frost and lightning damage bonus.

With this build, it is possible to achieve 55% fire damage bonus, 95% frost damage bonus, 50% lightning damage bonus and -25% mana cost.

Passives
Apart from the mentioned skills, you should also (try your best to) obtain these passive skills during your playthrough.

Divine Assistance
This passive skill is obtained by. It gives -10% mana cost and -10% stamina cost.

Internalized Lexicon
One of the skills in the Rune Sage skill tree. This skill and Runic Prefix are mutually exclusive (i.e. you can only choose one of the two). Internalized Lexicon eliminates the requirement of equipping Lexicon in your off-hand to cast runic spells, while Runic Prefix strengthen your Runic Magic by adding extra effects to them. Choose Internalized Lexicon for this build, because (1) this enables you to cast Runic Magic while equipping 2H weapons and (2) Runic Magic is not the main focus for this build.

Items
Apart from the mentioned equipment, you should also obtain these items.

Mage Tent
One of the best, if not the best tent for mages. It gives a buff of -15% mana cost to players after they slept in it. The buff lasts for a whopping 50 minutes long. It also reduces the Mana Burn rate from sleeping by 50%.

Alternative Breakthroughs
The Well of Mana is a nice-to-have breakthrough for every mage build, because Rune Sage is simply too good. You can swap skills and equipment at any time to adopt an entirely different mage build. For example, Hierophant (Lightning mage/priest) and the Cryomancer (Frost mage). While Leyline Connection and Shamanic Resonance are must-haves (so that you can obtain all Sigils), Well of Mana is NOT. You may consider other alternatives depends on your play style.

Spellblade's Awakening
The breakthrough of Kazite Spellblade. It increases your maximum health, stamina and mana by 15. More mana is always a good thing for mages. Also, it enables you to learn Elemental Discharge, a powerful ranged magaic which you can use to lure enermies.

Swift Foot
The breakthrough of Mercenary. It increases your movement speed by 10%. A nice skill for this build as you will be using hit-and-run tactics a lot. It also compensates the movement speed penalty given by Crimson Plate Set.

Alternative Weapons
The Thermal Claymore mentioned is great due to the damage bonus it offers. While you may also consider other alternatives depends on your play style.

Rotwood Staff
This staff provides -25% mana cost and gives 10% frost damage bonus. It allows you to cast spells more often without having to worry about mana consumption too much, while it gives less damage bonus than Thermal Claymore.

Combos
''Runic Protection, Runic Lantern, Warm, Cold and Blessed. You should make sure these buffs are always active.''

''When you spot an enemy, cast your Sigils before engaging. Cast the Sigil of Wind first because it has a channelling time.''

''Stand within the 2 Sigils (you don't have to re-cast the Sigils if they are both active.) and cast Spark will result in casting Fireball and Lightning Spark at the same time. This is your primary attack and Spark does not use any mana, spam it.''

''Stand within the 2 Sigils (you don't have to re-cast the Sigils if they are both active.) and cast Mana Push will result in casting Frost Push and Ethereal Bolt at the same time. This attack has very high Impact damage.''