Wizards tend to study the arbitrary and the more wonderful sides of magic. However many have focused their studies to the deadly elements of it, studying how best to utilize magic to swiftly and efficiently take down their targets. Wizards who have been abandoned, exiled, or otherwise by their colleges, abuse the arcane for their own selfish gain.

Spellcasting

Cantrips. You learn three cantrips of your choice from the wizard spell list. You learn another wizard cantrip of your choice at 10th level.

Spell Slots. The Arcane Assassin Spellcasting table(use the arcane trickster one) shows how many spell slots you have to cast your wizard spells of 1st level and higher. To cast one of the these spells you must expend a slot o the spell's level or higher. You regain all expended spell slots when you finish a long rest. 

Spellcasting Ability. Intelligence is your spellcasting ability for your wizard spells, since you learn your spells through dedicated study and memorization. You use your Intelligence modifier when setting the saving throw DC for a wizard spell you cast and when making an attack roll with one.

Spell Save DC = 8 + your proficiency bonus + your Intelligence modifier

Spell attack modifier = your proficiency bonus + your Intelligence modifier

Bonus Proficiency

When you choose this archetype at 3rd level you gain proficiency with Arcana.

Quiet Casting

Your cantrips that require a spell attack roll have the ability to deal sneak attack damage. If a cantrip does sneak attack damage it doesn't deal damage equal to its normal level scaling. In addition when you cast spells you have advantage on Dexterity (Stealth) checks on not being heard from the verbal components of spells.

In addition at 5th level your precise aiming of your spells adds an additional lethal element to them. When calculating damage for cantrips that require a spell attack roll you can add your dexterity modifier to the damage.

Magical Ambush

Starting at 9th level, if you are hidden from a creature when you cast a spell on it, the creature has disadvantage on any saving throw it makes against the spell this turn.

Silent Casting

Starting at 13th level you may completely ignore verbal components of spells. If you choose to use the verbal components of spells you may cast that spell at one level higher than the spell slot used to cast it. For example, when casting Witch Bolt with a 2nd level spell slot using the verbal components, you expend the 2nd level spell slot but cast the spell at 3rd level. When you cast a spell this way you automatically fail stealth checks from being heard from the verbal components of that spell.

Lethal Casting

Starting at 17th level all your spells that require a spell attack roll have the ability to apply sneak attack damage.

Your cantrips now regain there normal level scaling damage in addition to being able to sneak attack. For example, a firebolt will now do 4d10+9d6 on sneak attack.