Black Cat

Slinking through the shadows, a small tabby gracefully perches onto a low rooftop, watching the scene below. His master, clad in dark leathers, brawls with a pair of less than reputable gamblers they had rubbed the wrong way a few nights before. At his master's mental command, the tabby leaps through the air, the pale moonlight casting no shadow as it lands behind one of the thugs, slashing viciously at their calf. The thug cries out, spinning with fury and kicking at the cat. To his shock, it sinks into the shadow beneath them both, his strike missing wildly. As the cat reappears on his master's shoulder, they both purr with pleasure as his blade pierces the other bandit's throat, his body going limp. The remaining ruffian limps away as his leg continues to bleed, frost spreading from the wound. A few moments later, 3 guards approach the scene, dragging the gambler behind them. His crazy tale of a magic cat and his thief summoner goes unheeded, even as his friend's body reveals his valuables have mysteriously vanished. As the screaming gambler is pulled away, two happy felines sit and watch before soundlessly slipping back into the night.

Clowder

Beginning when you choose this archetype at 3rd level, you have a natural connection to the shadows and felines of the world. You have advantage on Wisdom (Animal Handling) and Charisma (Persuasion) checks when interacting with cats and cat-like creatures, Such as Tigers and Tabaxi.

In addition, you have a climbing speed equal to your walking speed.

Summon Shadow Feline

Also at 3rd level, you can manifest an echo of your own nature, a cat companion. You gain the ability to summon a shadow that assumes an animal form: as an action, you can cast the Find Familiar spell, without material components.

When you cast the spell in this way, the familiar appears identical to a Cat, and the familiar disappears after a number of hours equal to half your rogue level. Your familiar can attack, and acts on your turn. You can use this ability once per long rest. Your summoned familiar has several differences from a usual feline, and the statblock can be found below.

Crossed Paths

At 9th level, you learn to alter the balance of luck within your opponents and yourself, leading battles to more desirable outcomes. When you hit a creature with your Sneak Attack, that creature must remove an amount equal to your Intelligence modifier (minimum of 1) from any attack roll, ability check or saving throw they make. This will apply until they have made an amount of rolls equal to your Proficiency Bonus. 

In addition, your Sneak Attack no longer requires a Finesse or Ranged weapon.

Cat Burglar

At 13th level, you have learned to weave the shadows that form your familiar throughout your body, taking on their form. When your shadow feline is dismissed and not dead, you can use an action to alter your form to match theirs. You gain their damage and condition immunities, and can use their senses, traits and actions, except Void Drop. You may use their movement speed if it is higher than yours. Your game statisitics remain the same, but you will lose any equipment or armor not suitable for your new form, as your usual equipment melds into you. While in this form, you cannot summon your shadow feline. You will stay in this form until you are dropped to 0 hit points, killed, or spend an action to change back.

You can use this ability a number of times equal to your Proficiency Bonus per long rest.

Bag of Cats

At 17th level, the slinking shadows that bend to your will grow stronger, able to take multiple shapes at once. When you summon your Shadow Feline, two may appear instead, and using your Cat Burglar ability no longer requires you to dismiss your familiars.

In addition, you now gain access to the Void Drop reaction, and can use it to reappear within 5 feet of one of your shadow felines, provided one is within 60 feet of you. You do not need to be within dim light or darkness, being able to use your own shadow as well, unlike your familiars.

You can use this ability a number of times equal to your Intelligence modifier (minimum of once) per long rest.