3rd level — Bonus Proficiencies

Gain proficiency with the disguise kit and poisoner's kit.

3rd level — Assassinate

You have advantage on attack rolls against creatures that have not yet taken a turn in combat. In addition, a hit against a creature that is surprised is a critical hit.

9th level — Infiltration Expertise

With sufficient time and money, you can establish a convincing false identity complete with the supporting details needed to live under that identity.

13th level — Impostor

After studying another creature's behavior, speech and mannerisms, you can imitate that person much more convincingly.

17th level — Death Strike

When you hit a surprised creature, it must make a Constitution saving throw; on a failure, the damage of the attack is doubled.

How the features work together

The subclass has two distinct halves: combat ambush and long-form infiltration. Assassinate and Death Strike reward preparation before initiative, while Infiltration Expertise and Impostor reward campaigns where false identities, surveillance, and access matter. A party that coordinates stealth and encounter setup gets far more from Assassin than one that simply rolls initiative in plain sight.