Given Sunder Charm and Infinity have largely eliminated elemental immunity problems that players face in Hell difficulty, dual skill-tree builds for that Sorceress have grown to be less prominent in D2R; most opt instead to increase damage like a Lightning, Fireball, or Blizzard Sorceress’. For PvM however, single ability damage isn't necessarily the very best, and speed of clear can be established by a selection of factors, such as the “coverage” of the ability, and cast delay. Don’t forget, you can dual-wield Sunders at the cost of severe punishment for your resistance.

One overlooked feature from the Hydra/Orb Sorceress, maybe the stackable damage components which may be used simultaneously (you’re casting the spells at different points, however, Hydra continues to do damage while your Frozen Orb is casting. You would not have the ability to cast another Frozen orb, Blizzard, Lightning, or Fireball effectively throughout the Orb cast delay rendering them largely non-stackable. Frozen Orb and Hydra are generally low synergy abilities, meaning they might require less skill investment to optimize. By forgoing some synergy skill investment for every ability, you can still retain 60-80% of the effective damage of each.

Stats

This is a standard Non-ES sorc because there are not enough remaining skill points after your damage spells. As such, invest all of your points in vitality once you have enough strength and dexterity for gear.

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Skills

The following would be the core skills for any Balanced Damage Hydra/Orb Sorceress.

1 indicate all prerequisites

20 points to Frozen Orb

Enough points in Cold Mastery to achieve -150% Enemy Cold Resist (after gear and Battle orders)

1-20 points to Ice Bolt — synergy for Frozen Orb (adjust while you prefer for the damage profile)

1 indicate Frozen Armor

1 indicate Teleport

1 indicate Static Field

20 points to Hydra

20 points to Fire Mastery

1-20 points to Fire Ball

1-20 points to Fire Bolt

Orb Primary:

You can adjust your skill distribution according to your preferred damage profile. If you want to be an Orb primary sorceress, you can invest around 50 points to attain maximum damage and negative resistance with cold mastery. With less investment in Hydra synergies, this ability gets to be more supportive in the function.

Hydra Primary:

This is my preferred skill build given Frozen Orb’s significant CC effect with or without damage, which makes it a fantastic supportive skill to Hydra. Max orb but put only one into Ice Bolt, and enough into Cold Mastery for -150 Enemy Resistances. With only approximately 35 skill investments into the Cold Tree, you release significant skill points for the Fire Tree, helping you to build not just a strong Hydra, but an advisable Fireball too.

Gear

The following may be the recommended gear for that Hydra/Orb Sorceress:

Weapon: Heart from the Oak / Spirit runeword (cheaper alternative)

(If you're a primary Orb, you might consider Death’s Fathom, or Eschutas if you’re a Hydra primary)

Weapon Swap: Call to Arms and Spirit Monarch Shield

Shield: Spirit Monarch Shield with 35% Faster Cast Rate (necessary for breakpoint)

Body Armor: Chains of Honor / Enigma / Vipermagi / Ormus

Helm: Shako / 2/20FCR Circlet

Gloves: Magefist / Trangs

Boots: Sandstorm Treks/ Rare tri-res boots/ Aldurs / War Travellers

Belt: Arachnid Mesh

Ring 1: The Stone of Jordan or 10% FCR Ring

Ring 2: The Stone of Jordan or 10% FCR Ring

Amulet: Mara's Kaleidoscope or 2 skill x% FCR Amulet.

Charm 1: Sorceress Hellfire Torch

Charm 2: Annihilus

Charm 3: Cold Sunder

Charm 4: Fire Sunder

Charm 5: Cold Skiller and/or Fire Skiller Grand Charms with Life or Faster Hit Recovery to achieve the 86% (Optional Gheeds rather than 1 killer)

Charm 6: Small Charms with Life, Resistances, Mana, or Faster Hit Recovery based on needs

The double under discussion is essential as lowering two resistances with a significant margin is going to be detrimental to your survival efforts in the game. My recommendation is you select one, whichever you're leaning towards together with your damage profile, or whichever immunities you encounter more in your chosen farming destinations. Likewise, it's also important to explain that we are nearly always trying to attain the 105% FCR breakpoint, every higher becomes inefficient. If you do opt for that dual sunder build, you'll need more resistance from charms for dangerous areas. Thankfully Souls won't be a problem.

Faster Hit Recovery Breakpoints

Faster Cast Rate Breakpoints

Mercenary

You can pick between a Holy Freeze, Prayer or Offensive, or Might Act 2 Mercenary to accompany your Hydra/Orb Sorceress. Remember that Insight’s Meditation aura synergizes with prayer, and doubles its healing effect. The CC effect of holy freeze might not be necessary given Frozen Orb’s full-screen freezing power. A might aura isn't generally recommended while you shouldn’t be just a few the mercenary damage and therefore are primarily utilizing his weapon aura effect.

Weapon: Ethereal Infinity or Ethereal Insight

Body Armor: Ethereal Chains of Honor / Fortitude / Stone / Guardian Angel

Helm: Ethereal Andariel's Visage socketed having a Ral Rune

While Fortitude may be the standard Mercenary Armor, it isn't necessary once we are not optimizing Mercenary damage. Instead, survivability ought to be prioritized. My favorite option is an eth Guardian Angel for that huge boost to max resistances and it is affordability. Life leech continues to be an important sustain tool for any Mercenary, so Andariel’s Visage is usually recommended, along with a Ral rune socketed to offset its nerf for your fire resistances.