Revamped Assassin

This is not something that I came up with..

Tricks of the Trade

• At the 3rd level, gain proficiency with disguise kits, poisoner’s kits. Your proficiency with poisoner’s kits can apply to Intelligence (Nature) checks and Charisma (Persuasion) checks to obtain or harvest poisons. 
• Your resourceful efficiency allows you to craft disguises and poisons at half the cost and time required. You have resistance to poison damage due to your time spent building up your tolerance. You may also apply poison to a weapon or ammunition as a bonus action instead of an action. 
• Studying behavior has given you a cerebral ability to influence others. You may use your Intelligence modifier instead of your Charisma modifier when you resolve a Charisma-based skill check. 

Assassinate

Starting at 3rd level, you are at your deadliest when you get the drop on your enemies. You have advantage on attack rolls against any creature that hasn’t taken a turn in the combat yet. In addition, any hit you score against a creature that is surprised is a critical hit. You can also add your proficiency bonus to Initiative rolls.

Infiltration Expertise

Starting at 9th level, you gain proficiency with forgery kits. You roll skill checks with advantage to impersonate or adopt fictional personas or impersonate individuals if you observe the subject’s speech, handwriting, mannerisms, or other notable traits for ten minutes. Poison at night can be as deadly as an army at noon. You roll Sleight of Hand checks with advantage to avoid detection when poisoning food or drink. 

Just Business

At the 13th level, your Sneak Attack dice becomes d8’s instead of d6’s. Treat ones and twos rolled on your Sneak Attack dice as if they are threes. 

Death Strike

At 17th level, you master the art of killing or crippling enemies. When you attack and hit a surprised creature, it makes a Constitution saving throw (DC 8 + your Dexterity modifier + your proficiency bonus). Double the damage of your attack against any creature that fails this saving throw. Regardless of whether the creature passes or succeeds at this saving throw, its Initiative value in the turn order is reduced by 2d6 + your Dexterity modifier for the remainder of the combat encounter. .