Prowler

A third level archetype of Rogue. Its signature feature is moving through the space of any creature of a larger size category, and you can end your movement in another creature's space. A creature larger than you can choose to avoid giving you cover even though you are in its space if it is aware of you and able to move, although it doesnt have to use any of its movement to do so. 

Slinking Leap

You can use a bonus action to use the Help action to aid the next attack against a creature within 5ft of you. You can also use a bonus action to interfere with attacks against a target you can see. The first time a creature within 5ft of you attacks the designated target before the start of your next turn, it makes the attack roll with disadvantage.

While in another creature's space, you can use your action to attempt a Dexterity (Acrobatics) check contested by the other creature's Strength (Athletics) or Dexterity (Acrobatics) check (target's choice). If you succeed, you can knock it prone or cause it to drop a held item of your choice. If your mouth is free when you cause a target to drop a tiny held item, you can catch the item as it falls.

Underfoot

As long as you are in the same space as a creature of a larger size category than you, you have half cover against it. A creature larger than you can't avoid providing you with half cover against you other enemies, even if those enemies attack from multiple directions. You lose the benefit of this feature while you are unable to move. 

Fleeting Shadow

You have advantage on Dexterity (Stealth) checks to hide from vision and hearing. You can even confound magic that would reveal you by using your reaction when a spell or other magical effect would yield information about you. You know only that you are able to use this feature before you must decide whether or not to use your reaction. If you elect to use this feature, you learn what information the spell or effect would have revealed, and you can then choose to return no information at all or you can choose another creature you can see of a larger size; the effect yields comparable information about the creature you chose. 

Death From Below

As long as you are in a larger creature's space and an ally of yours that is not incapacitated is within 5ft of the larger creature, you have advantage on attack rolls against the larger creature whose space you share.