Maybe there's a reason you kill, were you adopted by a cult, or did you drown and nobody around you noticed or helped? There might be no reason, you could just be deranged, or bloodthristy, either way you scare and you kill.

You don a scary persona and wreak havoc by committing murders, leaving a trail bodies and terror anywhere that you go.

Killer's Persona

When you take this archetype at the 3rd level, you gain proficiency with a disguise kit, and can use this to make a signature mask and/or costume for your persona. Along with this you gain a one-handed melee weapon that you are proficient with. This weapon is now your signature weapon.

Signature Attack

You can use your signature weapon to do a signature attack, does 2d8 damage, no matter what the previous damage was, unless it was more, in which case it does regular damage, alongside that your victim must pass a DC 10+ your CHA modifier, wisdom check, or become frightened for 1 turn per CHA modifier, so if you have a +2 CHA, they're frightened for 2 turns.
This can be used once per long rest.

Shadow Step

At 9th level, when you are in dim light or darkness, as a bonus action you can teleport up to 60 feet to an unoccupied space you can see that is also in dim light or darkness. You then have advantage on the first melee attack you make before the end of the turn. 

You can do this 3 times per short rest.

Terrifying

When you reach 13th level, you are too scary for enemies to stay composed, and they trip over themselves.

You choose one frightened target. This target must pass a DC 10+your CHA modifier dexterity check or become prone for the next round.

You can do this 3 times per long rest. There is a 2 round cooldown.

One Last Scare

Starting at 17th level, you, the supposedly dead villain, comes back for one last scare

When you reach 0 hit points, after one death saving throw success you can go back to 5 hit points. You spend one turn pretending to be dead, next turn you can get up, frightening one target of your choice for however many rounds your CHA modifier is, so if your modifier is +2, they're frightened for 2 rounds.

You can use this once per long rest.