This is a homebrew warlock pact of my own writing. The current working title is "The Thunderous Being" but am absolutely open to suggestions.

Perhaps it was a strong air elemental, or an elder tempest from the elemental plane of air, or maybe a god of storms desires a little more than just your devotion. Whatever it is, you have struck a deal with a being of thunder and lightning in exchange for power.

Expanded Spell List

Your thunderous patron lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Thunderous Being Expanded Spells

Static Charge

Starting at 1st level, your patron bestows upon you an aura of slight static electricity out to 5 feet, just to remind you of their presence.

You learn the shocking grasp cantrip. It does not count against the number of cantrips you know and it is considered a warlock spell for you. It’s range is 5 feet for you rather than touch.

  At 5th level, both your auras range and the range of shocking grasp increase to 10 feet. At 12th level they both increase to 20 feet. Finally, at 17th level, both ranges increase to 30 feet.

Arc Flash

When you reduce a creatures hit points to 0 using a warlock spell or your pact weapon your speed increases by 10 feet for three rounds. If you kill another creature with a warlock spell or your pact weapon during that time, the countdown resets and your speed increases by another 10 feet.

Shock and Awe

As a reaction, whenever you deal lightning or thunder damage, you may halve the damage you deal to blind the target if the triggering damage is lightning or deafen the target if it is thunder for one round. If the triggering damage hits multiple creatures choose one of the damaged creatures to be affected by this ability. You can use this feature a number of times equal to your proficiency bonus before needing a long rest to regain this ability.

With Lightning Comes Thunder

You have become an indispensable asset to the goals of your patron. With that importance comes the need to protect you so you may continue being an instrument of their will. Your patron assigns to you a personal guard for you to call upon. As an action on your turn, you may summon an air elemental myrmidon, it takes its turn directly after you in combat and you must spend your bonus action to command it to take any action other than dodge. It can stay on your plane for 1 minute as the interplanar travel is taxing, if you are on the elemental plane of air it will stay with you until it's hit points fall to 0. Once it disappears, you can summon it again after 2 long rests.

I'm going to assume that you put the abilities in the order that we would get them with their level.

Static Charge - aura doesn't do anything other than exist. There is no mechanical benefit to having it. You've said that you get the shocking grasp cantrip at 5 feet which is the equivalent of being within melee of you, making it effectively no different. Of course, that changes as you level but needing to be 5th level to get use out of your basic warlock ability makes it not very worth taking at low levels.

Arc Flash - doesn't seem super useful either since warlocks have very limited spell slots, thought doing it with cantrips is cool. You also specify pact weapon, which requires that you'd take pact of the blade to get the benefits. You could argue the same about Hexblade, but Hexblade gives you the ability to choose an entirely different weapon as your hexblade weapon so its not reliant on having a specific pact even if it wouldn't make sense to do a different pact. Also, you have basically infinite movement here. Each creature you kill increases your movement speed by 10 feet which stays increased for 3 rounds or refreshes with another kill. A temporary 10 feet of movement isn't that great by itself since if you are in melee you'd still provoke opportunity attacks and if you are going ranged then the movement is more or less inconsequential since you won't need to be near people anyway, however having the effect stack is crazy. Cast a fireball on a group of undead and you are zooming. I think getting the movement speed bonus is cool, but after each kill, it requires that you are the one to kill the creature which isn't something that you can guarantee and if you aren't the one getting the kills you aren't gaining anything. Lastly, making it round biased means that if you roll badly on initiative it would disappear at the start of the round, making their situations where you don't get the full benifit. Usually, this is solved by saying something like "end of your next turn"

Shock and Awe - Seems like it would be good at low level with cantrips but once you start dealing any amount of damage you'd probably not want to use them, especially not at the cost of a spell slot and a reaction. Since you'd be cutting the damage you deal in half the stronger your attack is the less worth-it it will be to use the ability and since you should only be getting more powerful as you level its wouldn't really be worth using unless you roll bad damage. Also Being blind is much worse than being deafened since the blind condition imposes disadvantage on attacks made by the creature and advantage on attacks against a creature, while deafened just makes you fail checks that rely on hearing.

With Lightning Comes Thunder - seems pretty cool and all in all pretty good as a capstone. The only issue is there is a lot to do with your bonus action especally at high levels and using it to command a creature may not be better than an alternative. Also using an action to summon it and then having to use a bonus action on the same turn to make it do anything seems like it is probably a waste of your turn. The name is also a bit misleading. I assumed that if you did thunder damage you would do lightning damage aswell and vice versa because of the name. Perhaps, Storm companion or something to show that you are getting a friend in the name.

Overall - It seems very interesting. A lot of the ideas are unique in ways that I think with some tweaking and reworking would make a fun subclass to play.  I do worry about the fact that you have no way to improve your lighting/thunder damage at all as well as nothing that really does anything with it aside from Static Charge and Shock and Awe. If you were to face a creature that had resistance or immunity to lighting or thunder damage you are left a bit flat. There also is little reason to use those spells since even the effects that you have that augment them in some way don't add, but detract from the ability of those spells. It seems like a subclass designed around being in melee since you have aura and movement speed but there really is no benefit to being in melee with this subclass.

Recommendations -

• Define what place this subclass is supposed to be. Is it more melee or more ranged (or both) and make the abilities more suited to that playstyle.
• There needs to be more synergy with lighting and thunder damage. Make it really worth using those spells by giving them extra damage, extra effects, or potentially even making your melee attacks deal those kinds of damage.
• Give Static Charge an effect before level 5. I think making shocking grasp a multi-target spell that can target any creature within your aura equal to your charisma/constitution modifier would be a good solution for melee. I'm not sure what you could do for ranged, since it is an aura but I'm sure there is something that could be done.
• Arc Flash needs to be reworded. I think that making it something like when you kill a creature using lighting/thunder damage your movement speed is increased by 10 feet and you don't provoke opportunity attacks until the end of your next turn. Again, this works better for melee, but isn't terrible with range either.
• Shock and Awe needs to be more useful. you could make it blinded and stunned instead so both statuses give a mechanical benefit and definitely find a different trigger than a reaction to cut your damage in half. Maybe a reaction to force a saving through equal to the damage dealt or something. That will encourage dealing more damage and make it scale with you.

This is a really cool idea though. It definitely feels like something that could be real and could be fun to do. Just a little bit of reworking and making the language clearer and it is good to play!

For the Static Charge you could make it an effect that works similar to how nova cantrips (like sword burst, or word of radiance) work and even increase the damage (instead of the range) at 5th, 11th, & 17th levels. Kinda make it like it’s own special cantrip just for them that isn’t a cantrip but a built-in ability so it isn’t subject to things that affect spells or magic. That could be cool. It could even have a similar rider as shocking grasp.
     (If this was your intent by giving shocking grasp a range of 5 feet that didn’t come through. Just changing the range wouldn’t make it affect more than a single creature. You would have to instead change it to an AoE.)

Arc Flash’s benefit would make more sense since with the above change since most Warlocks have no real need for speed unless they are melee focused (which few are). But by keeping the range of the static small and making the damage scale it gives them a reason to want to zip in, zap, and zip out.

For Shock and Awe you could skip halving the damage and just have it apply the condition to a single creature.

Over all the whole thing needs a language pass (or two) to clean up the language and make it both more concise and more precise, but that’s what first drafts are for.

Thunderous Being V2 (name suggestions wanted)

Perhaps it was a strong air elemental, or an elder tempest from the elemental plane of air, or maybe a god of storms desires a little more than just your devotion. Whatever it is, you have struck a deal with a being of thunder and lightning in exchange for power.

Expanded Spell List

Your thunderous patron lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Thunderous Being Expanded Spells

Static Charge

Starting at 1st level, your patron bestows upon you a minor blessing of lightning. You learn the shocking grasp cantrip, it does not count against your number of cantrips known and it counts as a warlock spell for you. You have an aura of static electricity out to 5 feet, whenever you hit a creature with a melee weapon attack or with the shocking grasp cantrip, you may deal 1d6 of lightning damage to another creature within the radius of your aura.

At 5th level, your aura increases in range and in strength, your aura extends to 10 feet and the lightning damage increases to a d8. At 12th level, the aura extends again to 20 feet and the lightning damage increases to a d10. Finally, at 17th level, your aura extends out to 30 feet and the lightning damage increases to a d12.

Arc Flash

When you reduce a creature to 0 hit points using Lightning or Thunder damage your speed increases by 10 feet and your movement does not provoke opportunity attacks until the end of your next turn.

Shock and Awe

As a reaction, whenever you deal lightning or thunder damage, you may force one affected creature to make a constitution saving throw equal to the damage taken to blind the target if the triggering damage is lightning or stun the target if it is thunder until the end of their next turn. You can use this feature a number of times equal to your proficiency bonus before needing a long rest to regain this ability.

Thunder Companion

You have become an indispensable asset to the goals of your patron. With that importance comes the need to protect you so you may continue being an instrument of their will. Your patron assigns to you a personal guard for you to call upon. As an action on your turn, you may summon an air elemental myrmidon, it takes its turn directly after you in combat and you must spend your bonus action to command it to take any action other than dodge. You can give it it's first command using the same action you used to summon it. It can stay on your plane for 1 minute as the interplanar travel is taxing, if you are on the elemental plane of air it will stay with you until it's hit points fall to 0. Once it disappears, you can summon it again after 2 long rests.

I like it! Could use another pass over to make sure everything is clear within the language, but it seems to me like it is ready to playtest!

I agree with Conan, it looks like it’s ready to start playtesting it, but it needs some help with the language. Here’s a little help with the language; (the rest will come with playtesting):

Static Charge

1st-level Thunderous Being feature

Your patron bestows upon you a minor blessing of lightning. You learn the shocking grasp cantrip, it counts as a warlock spell for you, but does not count against your number of known cantrips.

In addition, you have an aura of static electricity that extends from you out to a distance of 5 feet. Whenever you hit a creature with a melee weapon attack or the shocking grasp cantrip, you can deal 1d6 lightning damage to another creature within the radius of your aura.

When you reach certain levels in this class the radius of your aura increases by 5 feet, and the damage die of your aura increases in size: 5th (10 ft., and 1d8 damage), 11th (15 ft., and 1d10 damage), and 17th level (20 ft., and 1d12 damage).

Arc Flash

6th-level Thunderous Being feature

When you reduce a creature to 0 hit points using Lightning or Thunder damage, your speed increases by 10 feet and your movement does not provoke opportunity attacks until the end of your next turn.

Shock and Awe

10th-level Thunderous Being feature

Whenever you deal lightning or thunder damage to a creature you can spend your reaction to force one affected creature to make a constitution saving throw, the DC for the save is equal to the damage taken by that creature. On a failed save the creature is blinded if the triggering damage is lightning damage, or stunned if it is thunder damage. The condition lasts until the end of that creature’s next turn. You can use this feature a number of times equal to your proficiency bonus, and you regain all use of this feature whenever you finish a long rest.

Thunder Companion

14th-level Thunderous Being feature

You have become an indispensable asset to your patron in the furtherance of its goals. With that importance comes the need to protect you so you can continue being an instrument of your patron’s will. Your patron assigns to you a personal guard for you to call upon.

As an action you can summon an air elemental myrmidon, it manifests in an unoccupied space that you can see within 30 feet. The creature is an ally to you and your companions. In combat, the creature shares your initiative count, but it takes its turn immediately after yours. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take another action. That action can be one in its stat block or some other action. If you are incapacitated, the myrmidon can take any action of its choice, not just Dodge. You can give it it's first command using the same action you used to summon it. 

The myrmidon remains for up to 1 minute if you are on any plane other than the elemental plane of air where it lasts indefinitely. The myrmidon immediately vanishes if it is reduced to 0 HP. Once you have used this feature you cannot use it again until you have finished 2 long rests.

1st Edit: Typos
2nd Edit: Added phrase.

You guys have been incredible thank you so much.

I was thinking about it and your Static Charge could probably scale for more damage at higher levels. Like adding a d6 at 5th, 11th, and 17th levels instead of incrementing the die size. And you might be able to get away with summoning the myrmadon every day since it only lasts for a minute (or until killed). Some things to consider while playtesting it at any rate. (See why playtesting is so important?) 

And I added a phrase to the wording of Thunder Companion I wrote for you. It’s highlighted with a pink underline.

I appreciate it very much!

This is so wholesome