Aspiring hero

You've taken many a wrong turn on this road, but slowly, you're finding you way back on the path you once dared to walk. 

• You are immune to the frightened condition so long as you are within 300ft of at least 1 ally. * Otherwise, you have advantage saving throws against frightened effects.
• When using the "know your enemy" class feature, you can identify the specific characteristics of the creature you're observing, as opposed to how they are relative to you. This can however be obstructed by illusions and other magical phenomenon. 
• You can reroll Nat 1s and 2s on Persuasion checks to negotiate, mediate, or otherwise resolve conflicts.
• lastly, when an ally who can hear you within 60ft of you makes an attack roll. As a reaction you can spend a superiority die to use one of your battle master maneuvers on your ally's attack.*

you gain this ability At level 11:

In Their Hour of Need: Once per long rest, as a free action, you can interrupt another creature's turn in combat to come to the aid of another in potentially mortal peril.

When another creature you can perceive is about to receive damage that will bring them to 0 HP, die, or suffer from a potentially fatal circumstance, such as falling into lava or tumbling off a cliff. You can interrupt the turn in which this is happing and take a full turn; you must use this turn to attempt to save the creature(s) in peril. If you can by any means save the creature from falling to 0 HP or befalling their perilous circumstance, on your turn that round you may act normally. If you fail to do so, you are stunned until the end of your next turn.

This ability can also be used outside of combat to avoid the same circumstance, but with no benefit or detriment for success or failure. 

Lastly, The DM has final say on when this ability can be used and what can be done to meet the criteria for saving the creature(s) in peril.