Duskwalker.

Many witches go through lengthy rituals to call forth specific spirits through the veil and into our world, but Duskwalkers have no time for such frippery. Their covens focus on speed and versatility, learning to adapt to situations as quickly as possible. Their practice allows them to summon the help of spirits almost instantly, without the use of lengthy and carefully cast spells, but this comes at a cost: a Duskwalker’s abilities depend entirely on whether they are bathed in light or in darkness. When standing in a brightly lit room, they can channel spirits that give them formidable defensive abilities and draw truth from lies and fabrication; when standing in darkness, they can meld with it, becoming one with the shadows as they wait to strike at the perfect time.
This dichotomy inherent in their specific practice of witchcraft defines them. Not only their arcane abilities but their entire beings are influenced by light and dark. As different spirits are called to their aid, by the whims of the light and the dark rather than their own choices, many of them experience subtle changes in their demeanour. Some witches of this practice even report feeling as if their body is occupied by two completely different people, who each take control depending on the light.
Duskwalker witches constantly walk the crepuscular line between darkness and light. Some become defenders, advisors, and seekers of truth, but just as many become infiltrators, spies, and assassins. One must wonder if the choice of where they stand is really theirs to make, or if their agency in this is just a trick of the light.

Witchmark.

Witchmarks for Duskwalkers tend to change depending on whether they favour light or darkness in their practice. Some have dark sclerae in one of their eyes to symbolize their existence between the two realms. Some have white smoke snaking up one of their arms and dark smoke up the other. The commonality between all Duskwalkers’ marks is that they all symbolize the duality in their witchcraft.

Level 3 Feature:

Initiate of Light and Dark.

When you choose this archetype at 3rd level, spirits of darkness and light influence your very being when you are in their domains.
The lighting in the space you are currently occupying dictates what abilities you can perform. You get access to different abilities depending if you are in darkness or bright light. When you are in dim light, you can choose between the abilities given by darkness and bright light. Once you’ve chosen, you cannot change your selection. Whenever you leave dim light and enter darkness or bright light, your choice is overpowered by the lighting you are standing in. If you leave a zone of darkness or bright light and re-enter dim light, you must choose again.

Crepuscular Combatant.

Starting at 3rd level, your demeanour in combat changes drastically depending on which spirits accompany you, relying on true strikes when bathed in light, and on underhanded tactics when submerged in darkness.
When in Darkness: As long as you are in darkness, you can use your Sneak Attack against a creature provided you don’t have disadvantage on the attack roll, you don’t need advantage on the attack roll or for another hostile creature to be within 5 feet of the target. All other rules for Sneak Attack still apply to you.
When in Light: Once per turn, you can reroll one die of your damage rolls. Once you’ve rolled, you must take the second roll.

Eyes of Twilight.

Starting at 3rd level, spirits reveal to you the world through unclouded eyes. Spirits of darkness let you see through their domain, and spirits of light expose the weaknesses of others.
When in Darkness: You are immune to the blinded condition and you gain darkvision out to a range of 60 feet. If you already have darkvision, its range increases by 30 feet.
When in Light: When looking at a creature that is also under bright light, you can use your bonus action to hear the truths whispered by the spirits of light. You know any damage vulnerabilities, resistances, or immunities it has.
You can use this feature a number of times equal to your proficiency bonus. You regain all uses of this feature after finishing a short or long rest.

Level 9 Feature:

Step of Dusk.

At 9th level, the way you walk through the world changes drastically. Light guides your steps and protects you from dangers on your path. Darkness envelops you, shielding you from prying eyes and allowing you to fade through it as if you were a shadow.
When in Darkness: As part of your movement, you can meld with the shadows and teleport yourself to an unoccupied space you can see within range. The space you teleport to must also be in darkness. Your range for this ability is half your speed. You can bring along objects as long as their weight doesn’t exceed what you can carry, but no living beings. This movement does not trigger attacks of opportunity. You can move this way a number of times equal to your proficiency bonus. You regain all uses of this ability after finishing a short or long rest.
When in Light: You can’t be slowed by difficult terrain, magical or otherwise, and you instinctively know if there are any traps within 30 feet of you. You don’t know the exact type of trap or its exact location, but you can determine whether it is magical, and what kind of damage, if any, it deals.

Level 13 Feature:

Penumbral Blades.

At 13th level, light and darkness dictate your attacks. Spirits of darkness ensure a deadly outcome to each strike you make, and spirits of light help your allies strike truer.
When in Darkness: When rolling damage, you can reroll all 1s. You must take the second roll.
When in Light: When a friendly creature that you can see and is within bright light rolls damage against another creature, you can use your reaction to make the target of that damage make a Wisdom saving throw (DC equals 8 + your proficiency bonus + your Dexterity modifier). On a failure, the attacker can roll your Sneak Attack bonus as part of their damage. The Sneak Attack damage type matches that of the initial attack; for example, if your ally was doing fire damage, the Sneak Attack damage will also be fire damage. You can use this ability a number of times equal to your proficiency bonus. You regain all uses of this feature after finishing a long rest.

Level 17 Feature:

Master of Light and Dark.

At level 17, you have mastered the shifts in the veils when you cross the boundary between light and dark, and can bend them to your will. As a bonus action, choose light or dark. When you do so, you emanate an aura of darkness or bright light with a radius of 5 feet. If it’s an aura of bright light, it creates an additional 5 feet of dim light beyond your aura of bright light. As a bonus action, you can switch from light to darkness or end the effect. In addition to affecting your surroundings, this also affects your abilities that are determined by light conditions, letting you take control over when you wish to use your light or dark abilities. You can only use this ability three times, and regain the ability to do so when you finish a long rest.