Zanassu, The Spider Demon
Your patron is Zanassu, a demon lord of spiders. He bestows powers similar to his servants, the Aranea that inhabit the Spider Swamp in Calimshan. The Aranea were humanoids who could shapeshift into a spider form or a hybrid form that granted web and poisonous abilities. These Warlocks have a natural aversion to fire and do not learn fire-based spells like Hellish Rebuke.

Proficiencies

• Medium Armor Proficiency
• Shortsword Proficiency
• Perception Proficiency
• Athletics Proficiency
• Poison Resistance
  

Eldritch Strike: Melee Attack Enhancement
You channel your Eldritch Blast through your main hand and off hand weapons to deal additional Force damage equal to your Charisma modifier.

• Dual wield compatible- Enhances main hand and offhand attacks
• Great weapons incompatible - Great weapons are too massive and dissipate the eldritch power.  Eldritch Strike and its effects will do nothing.
• Agonizing Strike: Level 6 - The Agonizing Blast invocation adds your Charisma modifier to Eldritch Strike as Force damage
  

Aspect of Aranea: Spider Abilities Spell
This spell grants you abilities similar to the Aranea's hybrid form. As your level increases, your abilities become more potent.  This long lasting spell is usable once per short rest.

• Spider physiology - You are able to jump farther and walk on webs without becoming ensnared.
• Spider Venom I: Level 4 - When you cast Poison Spray, you coat your weapons with Spider Venom, dealing 1d4 poison damage for 3 turns.
• Spider Venom II: Level 8 - When you cast Poison Spray, you coat your weapons with Spider Venom, dealing 2d4 poison damage for 3 turns.
  

Entangling Webs : Poison Spray Cantrip Enhancement
Your Poison Spray cantrip also covers the area with relatively weak but stick spider webs.   

• Cursed Webbing: Level 3- The primary target is cocooned with cursed webbing that holds them similar to the Hold spell, making them vulnerable to critical hits. 
• Webs: Level 3 - These weaker webs dissipate 3 times faster than those created by the Web spell.
• Infested Webbing: Level 10 - Cursed webbing is now crawling with of tiny spiders that bite and poison the target.  Melee attacks against the target can cause these spiders to spread to other targets.   This lasts for 2 turns and can be removed by fire or acid. 
  

The Nine Hells - Phlegethos 
Phlegethos is the circle associated with fire and and those whose souls burn with hatred or revenge are drawn to it.  It is jointly ruled by two archfiends, Fierna and Belial.  The Warlock receives power from both with Fierna granting intense hellfire based powers and Belial granting powers related to pain and fear.   Phlegethos Warlocks use the dueling fighting style, keeping their offhand free to focus infernal power and redirect it for attack and defense.   Most abilities require the offhand to be free.    Phlegethos is a place of suffering and punishment and these Warlocks must also suffer to wield this infernal power.   Some abilities require the Warlock to be on fire and others will set the Warlock on fire. They are fire resistant but only the most powerful achieve immunity from the flames.   Many incorporate spells like Armor Of Agathys and False Life to survive.

Proficiencies

• Medium Armor Proficiency
• Shortsword Proficiency
• Rapier Proficiency
• Scimitar Proficiency
• Arcana Proficiency
• Fire Resistance
  

Hand of Fierna: Melee Fire Sweeping Attack
You channel the power of Fierna and swing your flame blade in an arc of hellfire. The very ground is set ablaze in the wake of your fury.    This is treated as a main hand and offhand attack: 1 Action Point and 1 Bonus Action Point.

• Hand of Fierna: Level 1 -  You deal 1d6 Fire in an arc and inflict Burning on enemies.   Allies are not struck by the flame blade but the fire on the ground will affect them.  
• Hellfire Weapon: Level 1 -  Hand of Fierna ignites your main weapon with hellfire, dealing 1d6 instead of 1d4 fire damage for 4 turns.
• Backdraft: Level 1 - The intense heat from Hand of Fierna causes a backdraft that sets you on fire.
• Backdraft Removal: Level 6 - Your control of the Hand of Fierna prevents you from suffering from a backdraft.
• Blast Wave: Level 8 - The Repelling Blast Invocation adds a chance for Hand of Fierna to knock enemies down leaving them prone.
  

Obscuring Flames: Defensive Fire Manipulation Passive
While surrounded by fire, flames and smoke partially obscure you.  Attackers have disadvantage on attack rolls against you. Moving while burning or moving through fire on the ground will activate this ability.

• Obscuring Flames: Level 3 - Enemies will be at a disadvantage when attacking you.   You will appear blurred by the waves of heat
  

Belial's Agony : Melee Attack Enhancement
Belial's influence adds pain to your melee attacks.  The Hex spell can twist suffering caused by Belial's Agony can be twisted into healing the Warlock, emulating the sadistic ways of Belial himself.

• Belial's Agony: Level 4 - The Agonizing Blast Invocation adds your Charisma modifier as Necrotic damage to main hand melee attacks.
• Pleasure from Pain: Level 6 - When Belial's Agony strikes an enemy affected by Hex you recover health  equal to  Level + Charisma modifier 
  

Nether Walk : Short Range Damaging Teleport
You pass through Phlegethos and teleport to an unoccupied space brining the fury of hell with you burning the area where you reappear.  

• Nether Walk: Level 5 - Range: 6m.  Damage: Charisma modifier as Fire in a 3 meter radius.  This ability costs a bonus action.
• Harbinger of Belial: Level 10 - The flames from which you arrive act like a Symbol of Fear.  Enemies in this area have a chance to become frightened.