Scion Critical Hellfire Build [Occ/Ass]

Main Damage Output:
4L - Fireblast - Cast While Channelling - Firestorm - Concentrated Effect
5L - Elemental Focus
6L - Controlled Destruction (By the time you get a 6L you should have enough crit chance to negate this gems downside. However, if you're rich and bought yourself a 6L or got a lucky early drop I'd recommend Increased Critical Strikes until your gear is sorted)

Curse Application:
4L - Ball Lightning - Curse on Hit - Enfeeble - Warlords Mark

Power Charge Generator/Top Up:
4L - Ice Spear - Power Charge on Critical - Chain - Cold to Fire

Mobility:
3L - Lightning Warp - Less Duration - Rapid Decay

Defence:
3L - Cast When Damage Taken - Immortal Call - Molten Shell

Auras:
Haste
Discipline
Clarity

Really, just get high ES, Crit, Crit Multiplier and Resists.

Though the build is focused around a pair of The Consuming Dark in order to get 60% Fire to Chaos and some Poison damage. It also helps bypass Elemental Reflect and synergizes with the Witch Ascendency Chaos Resist debuff.

Other notable Uniques include:

Infernal Mantle For more Fire to Chaos as well as some crit (Not to mention +1 Fire Gems and additional Fire Damage). Be careful of the 100% spell damage taken effect though.

Voidbringer If you can manage the mana, these are superb for ES and Crit. However this build IS mana hungry so you may find yourself relying on Mana Flasks.

Bated Breath Nice belt for ES.

Similar to gear, you're looking for ES, Crit, Crit Multiplier and Fire Damage (In a pinch Chaos damage will also work).

Notable Uniques:

Survival Secrets Easy to get, 10% Fire Damage, 3 mana regen. All in all, a nice simple starter jewel.

Assassins Haste Another easy to get jewel, no damage increase but cast speed is nice. As is the regen. Another good starter jewel.

Eldritch Knowledge Not the best gem, but there's a socket that allows this to be +20% Chaos Damage which ain't too bad if you find it.

Izaro's Turmoil Well, that's a nice amount of Fire Damage! The Cold Damage is a nice bonus for your Ice Spears. However, it only drops from Lab so... You'll likely want to buy this (Or skip it in SSF) if you're not into that place.