I know there are many homebrew Witcher classes out there.  This is my attempt to make a Ranger Conclave that has the flavor of the Witcher without adding new mechanics for signs, Witcher decoctions, etc.  This is basically a reskin of the UA Deep Stalker, with spells that mimic Witcher signs subbed in for the ones the Deep Stalker has access to.

Witcher Ranger Conclave

Witcher’s Training

When you choose this Conclave at 3rd level, you gain proficiency with the herbalist’s kit and the poisoner’s kit.  You also gain proficiency in one additional Ranger skill, or, at your option, you may double the proficiency bonus for any one Ranger skill in which you are already proficient.

Witcher’s Eyes

At 3rd level, you gain darkvision out to a range of 90 feet.  If you already have darkvision, you increase its range by 30 feet.

Witcher’s Magic

You gain access to additional spells at 3rd, 5th, and 9th level.  Once you gain a Witcher spell, it counts as a ranger spell for you but doesn’t count against the number of ranger spells you know.

            3rd:      burning hands; charm person; shield

            5th:      gust of wind

            9th:      slow

Extra Attack

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

Witcher’s Constitution

At 7th level, you gain proficiency in Constitution saving throws.

Witcher’s Flurry

Starting at 11th level, once on each of your turns when you miss with an attack, you can make another attack.

Witcher’s Dodge

At 15th level, when an attacker that you can see hits you with an attack, you can use your reaction to halve the attack’s damage against you.

Fits well with the Witcher theme.  Have you put any thought into what level 13, and 17 spells you would like in the bonus set? Having three extra level one spells is a bit lopsided.  The shield spell definitely, but drop the fire and charm and move them to the missing levels.

13th Compulsion

17th Flame Strike

Lets you keep the elemental type of the witcher (if not the order you would learn them in).  For the Witcher's eyes their is a similar trait on the gloomstalker that extends to 60 ft and gives +30 if you already possess darkvision.  Or perhaps mimic the Warlock Devils Sight and be able to see in magical darkness as well.  

Constitution and Flurry look good.  Witcher's dodge, I'm not sure about.  Few things utilize your reaction, this would pretty consistently mean half damage to a single attack in each round of combat vs any damage type.  Between Shield to avoid attacks, and the Dodge to halve attacks.  I think that would be a playtest thing to see if maybe you want it to only apply to only certain attack types.  Aside from either limiting the number of uses per rest, or the types it works against like physical or magical.  Might not be as strong as i think it is but definitely give it some playtest, see how much damage you can avoid each round of combat.  Had an idea, maybe you can use it a number of times in combat equal to your constitution modifier.  Food for thought.

And one parting shot, no need to list the extra attack since it is part of the main class.

I hope you like how the Duskblade has been working for you.  

edit:  I had that moment where I realized it was exactly like rogues uncanny dodge (thanks critical role for reminding me).