Specialties:

Pro: Infiltration, Initiative, Exceptional Singular Burst Potential
Con: Concentration, Weak against numbers.

Focus

Starting at 3rd level, if you spend at least 1 minute focused on another creature outside combat, you can gain concentration on said creature.
While focused on a creature in this way you cannot concentrate on other spells.

First Move

Starting at 3rd level, you have advantage on initiative rolls.
Additionally at 9th level whenever you make an initiative roll, you can treat a d20 roll of 9 or lower as a 10.

First Strike

Starting at 3rd level, you are at your deadliest when you get the drop on your enemies.
Any Melee Attack you score against any creature that hasn’t taken a turn in combat yet is a critical hit in the first round.
Any Ranged attack gains advantage against any creature that hasn’t taken a turn in the first round.

Starting at 9th level the above persists further only for your focus as long as you have concentration.

Know Thy Enemy

Starting at 9th level, if you spend at least 1 minute observing or interacting with another creature outside combat you can learn about another creature's combat capabilities compared to your own.
At the DM’s option, you might also realize a unique trait of the creature.
The DM tells you if the creature is your equal, superior, or inferior in regard to two of the following characteristics of your choice:

• Class levels (if any)
• HP
• AC
• 1 Stat

Once per turn you may spend half your movement speed to learn 1 of those characteristics during combat.

Additionally at 13th level, you can unfailingly create false identities for yourself of interest to your focus.
You must spend seven days and 25 gp to establish the history, profession, and affiliations for an identity. You can’t establish an identity that belongs to someone else.
Thereafter, if you adopt the new identity as a disguise, other creatures believe you to be that person until given an obvious reason not to.
Additionally for your focus you gain the ability to unerringly mimic speech, writing, and behavior. To do so you must spend three long rests studying components of the person:

• Speech
• Mannerisms
• Handwriting
• Personal Possessions
• Social Circles
• Residence

Your ruse is indiscernible to the casual observer. If a wary creature suspects something is amiss, you have advantage on any Charisma (Deception) check you make to avoid detection.
You gain advantage on (Insight) checks against your focus.

Cunning Strike

Starting at 13th level you’ve developed cunning ways to use your Sneak Attack. When you deal Sneak Attack damage, you can add one of the following Cunning Strike effects.
Each effect has a die cost, which is the number of Sneak Attack damage dice you must forgo to add the effect. You remove the die before rolling, and the effect occurs immediately after the attack’s damage is dealt.
For example, if you add the Poison effect, remove 1d6 from the Sneak Attack’s damage before rolling.

If a Cunning Strike effect requires a saving throw, the DC equals 8 plus your Dexterity modifier and Proficiency Bonus.

Poison (Cost: 1d6): You add a toxin to your strike, forcing the target to make a Constitution saving throw. On a failed save, the target has the Poisoned condition for 1 minute.
At the end of each of its turns, the Poisoned target repeats the save, ending the effect on itself on a success.
To use this effect, you must have a Poisoner’s Kit on your person. or an additional die

Disarming Attack (1d6): Attempt to disarm the target, forcing it to drop one item of your choice that it’s holding. The target must make a Strength saving throw. On a failed save, it drops the object you choose. The object lands at its feet.

Lunging Attack (1d6): Increase your reach for that attack by 5 feet.

Withdraw (Cost: 2d6) Immediately after the attack, you move up to half your Speed without provoking Opportunity Attacks.

Pushing Attack(1d6): If the target is equal or different in size to you by 1 category, it must make a Strength saving throw. On a failed save, you push the target away from you 5 feet for every d6 spent up to 15 feet.

Trip (Cost: 1d6): If the target is equal in size to you or increase the cost by 1 die for every 1 category of difference. It must succeed on a Dexterity saving throw or have the Prone condition.

Death Strike

Starting at 17th level, you become a master of instant death. When you attack and hit a creature that is surprised, it must make a Constitution saving throw (DC 8 + your Dexterity modifier + your proficiency bonus). On a failed save, double the damage of your attack against the creature.