The PHB version of the Assassin is one of the most iconic Rogue archetypes in all of fantasy, however, when you actually look at the subclass and dive deeper into it, it unfortunately falls short of that fantasy that many of us seek. And this class isn't the only one. I've begun looking at reworking various official subclasses that fall short of the fantasy that we all wish they brought, and trying to bring some minor, and sometimes major, changes to these archetypes in hopes that they can become slightly better, and improve when compared to the "over powered" subclass options available, giving players who care about creating the best statistical character possible, more options, rather than just pigeon-holing them into one subclass (I'm looking at you Moon Druid and Hexblade Warlock). So here is my take on the Assassin Rogue subclass.

You focus your training on the grim art of death. Those who adhere to this archetype are diverse: hired killers, spies, bounty hunters, and even specially anointed priests trained to exterminate the enemies of their deity. Stealth, poison, and disguise help you eliminate your foes with deadly efficiency.

Overview/Notes:

Assassin's Tools: Most players who play an Assassin Rogue never took advantage of these proficiencies, because they were often quite obscure and would just sometimes not really be relevant. So I implemented a change I believe should have always been there in giving the Assassin essentially Expertise with both of these tools, making their use more incentivized and relevant.

Assassinate: There are always so much confusion over what caused surprise and what didn't and it made this feature either incredibly broken when new or inexperienced DMs would rule it, or practically useless when more experienced DMs who were wary of crits would rule it. So I changed the wording of the ability a bit to make it more clear when assassinate could be triggered, without it being broken. And I also added the advantage on attacks against a creature that was poisoned using one of your made poisons, to incentivize the tool proficiencies a little more, and create some more strategy and forethought at the table.

Quick Blade & Infiltrator: The biggest turn off to the Assassin was it's 9th and 13th level features. They were in essence "non-abilities" because they were things that literally any character could do, and could do very well, but also often times would just be unnecessary or useless. You didn't really feel like and assassin or infiltrator with it before, so I changed the 9th level features to give you more success in triggering your assassinate ability instead with the increased initiative bonus, and infiltrator still allows you to carry through the essence of what the original feature was supposed to be, just in a more clear and deliberate way.

Caught Off Guard: Arguably the Assassin's worst feature was their previous level 13 ability. My rendition again, focuses on reinforcing the assassin fantasy we all want to play, giving the players more options to be the edge lord in the corner we all want to be. My goal with this feature is to give additional credibility to the ambush style attack pattern of the assassin rogue.

Death Strike: Death Strike is the only ability I didn't change. It feels good as it was, and is a level 17 feature, so it should feel powerful, except now it's just not as clunky thanks to the changes to Assassinate I am recommending.

Any and all feedback is welcome, and I'd love to hear your thoughts on my take on the Assassin Rogue Version 1 and hope you'll consider playing it at your tables.

Assassin's Tools

When you choose this archetype at 3rd level, you gain proficiency with the disguise kit and the poisoner's kit. Your proficiency bonus is doubled for any ability check you make that uses either of those proficiencies.

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 or is under the effects of a poison you concocted using your poisoner’s kit. In addition, when you take the Attack action, if you score a hit against a creature that hasn’t taken a turn in the combat yet, it is a critical hit.

Quick Blade

At 9th level, you can now add your proficiency bonus to your initiative rolls.

Infiltrator

Also at 9th level, you have advantage on Charisma (Deception) checks when trying to pass yourself off as someone else and gain a climbing speed equal to your walking speed.

Caught Off Guard

At 13th level, you have advantage on Dexterity (Stealth) checks while in dim light or darkness, and when you have advantage on a weapon attack roll, your weapon attacks score a critical hit on a roll of 19 or 20.

Death Strike

Starting at 17th level, you become a master of instant death. When you attack and hit a creature that hasn’t taken a turn in the combat yet, 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.