Monks rarely take part in assassinations, and even more rarely are the Assassin in that situation, these guys are one of the exceptions, excellent at moving stealthily, and excellent at taking out targets, they like daggers for their speed, but other weapons work as well.

Sneak Attack

You can find weak spots in an opponent when they aren’t focused on you, dealing extra damage when hitting. 

Assassination Expert

You are a master of assassinations, though not the best, you have made custom ways of fighting, and you’re good enough you will usually land most attacks you make.

Bladed Flurry

You gain an extra attack.

Evasive Mastery

You gain a +1 bonus to your unarmored AC and you can use the rogues uncanny dodge ability.

Ki Assassin

You can use your Ki to help assassinate, you can spend 1 Ki point to add 1d6 to an attack roll.

Team Buffs

You are confident in battle, and that can inspire your allies to fight longer or harder, and completely focus on the enemies ahead.

Assassins Unarmored

You’re a fast attacker, and a speedy guy while wearing no armor, you know how to protect yourself by moving fast, while not wearing armor.

Resistance Breaker

Your ability to use your weapons to the maximum of their limits lets you get through spots that most others would have trouble going through.

Luck For The Lucky

You’re naturally lucky somehow, not exactly sure why, are there any halflings around or something?

Target Slayer

You can target in on a person that you intend to kill, that person will have a hard time against you for sure.

Mage Warrior

Your Ki is specifically focused to absorb magic from things around you, increasing the amount of Ki you have

Accurate Shots

You gain a large bonus too to hit rolls

Skilled Assassinator

You gain a skill in two proficiencies of your choice, expertise in two skills of your choice, and options for assassins.

Clear Minded

You become immune to physic damage and the charmed and frightened affects.

Close Combat Fighter

You gain a bonus to unarmed strikes, a few custom melee attacks, and if you’re within 5 feet of an opponent and they miss an attack you may use a reaction to do an unarmed strike against them.

Evasive Skills

You gain a +1 to unarmored AC

Tank Assassin

You get a small HP buff a level.