i am running a low magic campaign soon and i have a player who wants to play an assassin rogue. we both felt it was lacking so i took a stab at writing one up that scales better and fulfills the feeling of a deadly combatant that strikes fast and hard without relying so much on actually surprising a foe.
Rogue Assassin version 2.0
will enter Flavor text

Spoiler: assassin 2.0
Starting at 3rd level, you are at your deadliest when your enemies are caught unprepared.
• You have advantage on attacks rolls against any creature that has not taken a turn in the combat yet. In addition, if you deal any damage with sneak attack during your first turn you deal maximum damage with sneak attack.

Bonus proficiencies
When you choose this archetype at 3rd level, you gain proficiency with the disguise kit and the poisoner’s kit. If you already have proficiency in either tool you can choose a new one instead of it.

Infiltration expertise
Starting at 9th level, you can unfailingly create false identities for yourself quickly.
• You have advantage on charisma(deception) and charisma (persuasion) while wearing a disguise maintain a false identity.
• You can make and don a new disguise with unerring speed. You can now create a new disguise in a minute and use your cunning action to don or doff one of your disguises.
• You can now carry up to 5 disguises on you at one time without drawing undue attention.

• At 13th level, you gain the ability to unerringly mimic another person’s speech, writing, and behavior. You gain a bonus to any check to avoid detection while wearing a disguise mimicking a person you have spent at least one hour observing. You gain a +1 bonus to these check for every hour you spend observing there behavior up to your intelligence modifier minimal of one.

Death strike
• Starting at 17th level, you become the master of instant death. The firs attack you make against a creature during a combat is a critical hit.

is there any glaring issues i over looked?