Feral

Ferals are instinctive survivors, embodying the savage fury of a wild predator. These rogues do whatever is necessary to survive when it comes down to it. Ferals will gnaw off their own arm to escape in the very second it becomes the best option. You fight like a wild wolverine; a cornered rat. Right when your foe thinks they have you, you are at your most deadly. 

Savage Striker

Starting at 3rd level, you begin to fight more like an animal than a man; fighting with tooth and nail rather than with a weapon. You can use Dexterity instead of Strength for the attack and damage rolls of your unarmed strikes, and when you make an unarmed strike on your turn, you can make an additional unarmed strike as a bonus action. Your unarmed strikes are considered a finesse weapon for the purpose of sneak attack.

Vicious Backlash

At 3rd level, you unleash your animalistic fury on any creature that dares to strike you. When a creature makes an attack roll against you, you can use your reaction to move up to 15 feet towards the creature and make an unarmed strike against them. You take the reaction after the attack, whether it hits or misses. 

Cornered Rat

Starting at 9th level, you fight even more fiercely when you are forced into a bad position. When you have less than half of your maximum hit points, you have advantage on all melee attack rolls, and your movement speed increases by 20 feet.. Additionally, your strange nature also means you can avoid effects that could weaken you. If you would be targeted by a spell or ability that only affects a certain creature type, you can treat your creature type as beast to potentially avoid the effect. 

Bestial Cunning

By 13th level, you are near impossible to catch. Your walking speed increases by 10 feet and you gain a swimming and climbing speed equal to your walking speed. You can escape a grapple as a bonus action, and you have advantage on saving throws made to resist the paralyzed, stunned and restrained conditions.

Go For The Throat

When you reach 17th level, you know how to defend your vital areas, and know when to go right for your opponent's. Whenever you make a successful unarmed strike against a creature which is prone, stunned or restrained, you can choose to turn that hit into a critical hit. Once you use this feature twice, you can’t use it again until you finish a short or long rest. 
Whenever a creature attacks you and lands a critical hit, you can treat it as a normal hit.