Notable Passives:

The Mage Skill Tree grants you the most basic modifiers, although they are instrumental to have. You will gain plenty of Intelligence, Resistance, and Cast Speed. The Warden grants you a lot of Ward Retention. The Knowledge and Destruction Notable is great for improving your Critical Strike Chance and Damage. 

Sorcerer Skill Tree (27 Points)

Notable Passives:

The Sorcerer Skill Tree unlocks your access to the Static Orb Skill. You will also gain lots of Cast Speed, Movement Speed, and Damage just from continuously Casting your Spells, which you will do all the time. The Rift Bolt grants you a lot of Health Leech from the Lightning Damage, but you can skip it if you can get Health Leech from another source. 

Notable Passives:

The Mental Catalysis and Inscribed Instruments are very strong notables that encourage you to use a Wand and Catalyst as your Weapons. The Runeword: Cataclysm greatly improves your Critical Strike Chance and Damage against enemies on Low Life. The enhanced effect of the Decree of the Burning Wind will be almost always active, giving you 10% more Damage against Bosses. The Jagged Veil will generate a lot of Ward, as you will Hit your Enemies very frequently, and it also improves your Damage with Critical Strikes. You can pick up the Celestial Doom to get very valuable bonuses, but only if you are sure to always apply the Brand on your Enemies. 

Your Passives will grant you a lot of Ward Generation and Retention, but only a little bit of Health. You will also get a lot of Intelligence, which allows you to focus your Items on Dexterity instead. The abundance of Cast Speed bonuses is also very impactful. You will be scaling your Damage primarily via Critical Strikes, however, applying Ailments such as Shock is still beneficial, due to interactions with your Sphere of Protection and the Mad Alchemist's Ladle. If your Mana sustain is not sufficient enough, you can sacrifice some Damage in favor of the Rune of Renewal or Decree of Bountiful Ocean Notables. 

Runic Invocation - your main source of Damage is the Runic Invocation. The Plasma Orb created using the Fire, lightning, and Fire combo deals the most Damage in this Setup, but if you happen to use a different Rune combo, it will still deal plenty of Damage. 
The Runic Energy causes you to accumulate stacks over time that will be consumed when you cast this Skill to improve the Damage and grant you a chance to repeat this Skill for free. The Word of Rahyeh grants you plenty of flat Spell Damage, which is very important to scale your Damage. The Word of Lagon greatly improves your Critical Strike Chance, but you can focus your additional points on the Elemental Lore or Unbridled Ruin more. 

Runebolt - to generate correct Runes you will use the Runebolt Skill. It deals a small amount of Damage, but can grant you Mana on Hit thanks to the Arcane Restoration Notable. The Runeweaver and the connected Notables will grant you a lot of Damage, Crit Chance, Mana, and Ward generation. The Arcanist grants you even more Cast Speed, and the Arcane Overcharge improves your Mana recovery by increasing the total amount of Hits. The Searing Dart is a very important notable that disables the Cold Bolt, which allows this Skill to grant you the correct Rune order for the Invocation on its own. 

Teleport - it is your main Traveling Skill. It is undoubtedly one of the best Skills in the game for movement, as it instantly teleports you to the desired place.  
Thanks to the Teleport's Skill Tree you will have lots of protection after using that Skill. The Ether Barrier, Out of Body, and Out of Mind grant you tons of Ward for casting the Teleport, and the Stable Bubble grants you Ward Retention which affects all your other sources of Ward too. The Time Dilatation doubles the duration of those bonuses, so you can have them permanently as long as you use this Skill frequently enough. 

Flame Ward - this is probably the strongest defensive Skill in the game, you should use it often. It grants you a lot of Ward and significantly reduces the Damage you take during its effect.
The Dual Aegis grants you an additional Charge, so you can use it more often. The Astonish automatically triggers this Skill when you are Stunned, but you can use it manually too, allowing you to better adapt to the situation. The Barrier and Prismatic Buffer are responsible for the great Damage mitigation of this Skill. 

Static Orb - in this Setup, this Skill deals a minuscule amount of Damage, but using it provides you with a Cold Rune if needed. Thanks to the Static Armor, using this Skill grants you a Lightning Aegis buff for a short duration, which slightly improves the Lightning Damage you deal, and reduces the Damage you take. You will need the Biting Force Notable to convert it to Cold, as by default it is a Lightning type. 

Stat priority:

On your Rare Items and Legendary Potential bonuses, you should seek Dexterity, Intelligence, Critical Strike Chance and Multiplier, Spell Damage, and Cast Speed. Any flat Spell Damage is also useful to have, as in this Build you don't focus on a particular Element.  You should always use a Wand and Catalyst as your Weapons. To improve your survivability you should aim for Health and Intelligence, as well as capping your Resistance. The Ward Retention or Ward Decay Threshold is also very important, although it can be rarely sourced from your Items. 

1. Dexterity
2. Intelligence
3. Critical Strike Chance and Multiplier
4. Spell Damage 
5. Critical Strike Avoidance 
6. Health 
7. Resistances 
8. Armor 
9. Movement Speed 

Recommended Unique Items: 

+(8% to 48%) Chance to Slow on Spell Hit +(8% to 48%) Chance to apply Frailty on Spell Hit +(8% to 48%) Chance to Shred Armour on Spell Hit +(8% to 48%) Chance to Electrify on Spell Hit +(8% to 48%) Chance to Poison on Spell Hit 6% more Spell Damage per Negative Ailment on the Target (up to 8) +1% increased Cast Speed per 2 Intelligence 1 Mana Gained on Potion Use per 4 Intelligence

Mad Alchemist's Ladle - this Unique Wand offers you insane amounts of Damage by stacking 8 Negative Ailments on your Enemies, which you will apply very quickly. It also greatly improves your Cast Speed. It lacks a flat amount of Spell Damage, which is why you will have to get it from other sources.

+(1 to 3) to Level of Runic Invocation (18% to 36%) more Damage while using a Wand for Invocations with Heo as their first Rune (18% to 36%) more Damage while using a Staff for Invocations with Gon as their first Rune (18% to 36%) more Damage while using a Sceptre for Invocations with Rah as their first Rune 3% more Damage per Strength for Invocations with Heo as their second Rune 3% more Damage per Dexterity for Invocations with Gon as their second Rune 3% more Damage per Attunement for Invocations with Rah as their second Rune

Fundamental Criterion - it is probably the best Armour for every Runemaster that uses any combination of Runes. You could use a Sceptre to further improve your Damage, but it will be hard to find a Sceptre that could outperform your Wand. The 3% More Damage per Dexterity bonus and Levels for Runic Invocation are strong enough to use this Armour over anything else. 

(30% to 100%) increased Freeze Rate Multiplier (10% to 20%) increased Movement Speed +1 Cold damage to Attacks and Spells per point of Dexterity -1% Physical and Cold Resistance per point of Dexterity

Mourningfrost - this pair of boots further encourages stacking the Dexterity, as it will grant you tons of flat Cold Damage for your Spells, on top of the More Multiplier you get from the Body Amour. However, as you obtain more Dexterity and Damage you must also gain more Cold and Physical Resistances on your remaining gear.

(5% to 8%) of Current Health converted to Ward when you directly cast a Necrotic Spell (5% to 8%) of Current Health converted to Ward when you directly cast an Elemental Spell +1 to Level of Necrotic Spell Skills +1 to Level of Elemental Spell Skills +(10 to 16) Strength (10% to 16%) increased Cast Speed

Twisted Heart of Uhkeiros - the additional Cast Speed and Spell Skill Level are quite useful on their own, but the main reason to use this Relic is the absurd amount of Ward you gain every time you Cast a Spell. Thanks to the Health Leech you will have an endless supply of Health to convert. 

+150 Armor +(6 to 13) Dexterity +(6 to 13) Intelligence +(35% to 65%) Necrotic Resistance 1 Ward per Second per 3% uncapped Necrotic Resistance

Boneclamor Barbute - this helmet grants you the two Attributes you care about the most, a decent amount of Necrotic Resistance, and plenty of Ward regeneration. Thanks to the Legendary Potential options you can amass double the amount of Dexterity the regular Rare Helmet could provide. 

Idols:

You can get an absurd amount of Cast Speed on your Large Arcane Idols, as long as you keep your Lightning Aegis active. Those can also provide you with lacking Resistance. You can also fit in two Adorned Arcane Idols that grant you a decent amount of Ward Retention, and even more Resistance or Health. 

Recommended Blessings:

• The Black Sun: you will have a lot of valuable options to choose from here. You can pick up Critical Strike Chance or Multiplier, Void Resistance, Health Leech, or Ward Decay Threshold.  
• The Age of Winter: in this Timeline you can obtain very potent bonuses for either Physical or Cold Resistance. Endurance or Armour is not very useful in this Build. 
• Spirits of Fire: there are only two useful bonuses here, the flat Armour or lots of Fire Resistance. The Endurance does not affect the Damage you take to Ward.  
• Reign of Dragons: it is very important to reach 100% Crit Avoidance, and this Timeline offers great help with that. If you happen to get it via your Gear, you should pick additional Resistance instead.  
• Ending the Storm: tanks to bonuses available here you can improve your Ward, or get lacking Lightning Resistance. The Lightning Shred is not that good since you will deal all 3 Elemental Damage types. 

END NOTE

This is the release version of our Plasma Orb Runemaster Build for Last Epoch, which focuses on one of the powerful Runic Invocations available for this Class. We had amazing results with the final form of this Build, and we can attest you won't be disappointed with it. If you enjoy high bursts of damage and don't like to worry about mana management, you have to try out this Build! Future Patches can change the performance of this Build, we will keep our eyes on it and update this guide accordingly to the game's growth.