you are unmarked no magic no special skills to others you seem to fade into the background

Level 3: Self Taught

You gain another Fighting Style feat of your choice.

when you use 2 weapon fighting while having additional arms you can attack with all of them

Level 7: Pay Attention

Thanks to you being required to pay attention to details your all ways ready , you have Advantage on Initiative rolls

In addition, immediately after you score a Critical Hit, you can move up to half your Speed without provoking Opportunity Attacks.

Level 7: Weakness Spotting

Your attack rolls with weapons and Unarmed Strikes can score a Critical Hit on a roll of 19 or 20 on the d20.

Also you may use a bonus action to discern a number of the following things equal to your wisdom bonus, you can do this to multiple creatures at once but only a number equal to your proficiency bonus

• Current HP
• Armor Class 
• Vulnerability's
• Immunity's
• Resistances

Level 10: Indominable Will

Because of Your will to get stronger your mind can not be read and you have advantage on wisdom saves 

and whenever you drop to 0 for you can instead drop to one hp you can do this a number of times = to your con modifier

Fighting Spirit

Blood frenzy: you have advantage ageints creatures not at full hp

Hit and weave: when you hit a creature you impose disadvantage untill the start of your next turn

Level 18: To Busy To Die

Defy Death. You have Advantage on Death Saving Throws. Moreover, when you roll 18–20 on a Death Saving Throw, you gain the benefit of rolling a 20 on it.

Death Is Not Rest: while maiing death saves you cab still use your actions untill you fully dead