Prehensile Feet. The simian's feet possess prehensility, the ability to act and grasp just like their hands.

Prehensile Tail. The simian can use its tail to interact with objects such as magic items, potions, light weapons, doors, etc. It is not as strong as their hands or able to perform fine motor tasks like picking a lock or writing well.

Alert. The simian has an additional +8 bonus to initiative, advantage on initiative, and cannot be surprised.

Ethereal Step. The simian can use 5 ft of its movement to step into or out of the Ethereal Plane. The simian has advantage on its first melee attack when stepping out of the Ethereal Plane unless the creature can see into the Ethereal Plane or has some other feature that would negate this.

Assassinate. The simian has advantage on any creatures that have not taken its turn in initiative. Additionally, attacks that hit creatures that are [Tooltip Not Found] are automatic critical hits.

Sneak Attack. Once per turn, the simian can add an additional 8d6 points of damage to an attack that they have advantage of or have an ally within 5 ft. of the creature.

Leaper. The simian's jump distance is tripled, and can use Dexterity in place of Strength when calculating its jump distance. 

Multiattack. The simian can make two attacks with its Quarterstaff of Darkness, two stunning strikes, and 1 feature with its tail strike.

Quarterstaff of Darkness. Melee Weapon Attack: +10 to hit, reach 10 ft., single target. Hit: 14 (1d10 + 6) magical bludgeoning damage and 5 (1d6) necrotic damage. On a hit, a creature has magical darkness fill their eyes, and the creature becomes blinded until the end of their next turn. If the creature can see through magical darkness then they are unaffected by this.

Stunning Strike. Melee Weapon Attack: +9 to hit, reach 5 ft., single target. Hit: 11 (1d8 + 5) magical bludgeoning damage. On a hit, the creature must make a DC 17 Constitution saving throw or become stunned until the end of the simian's next turn.

Tail Strike. Melee Weapon Attack: +9 to hit, reach 5 ft., single target. Hit: 11 (1d8 + 5) magical bludgeoning damage. On a hit, the simian can choose one of the following effects in place of doing damage:

Sweeping  Strike:  the creature must make a DC 17 Dexterity saving throw or become prone.

Disarm: the creature must make a DC 17 Strength saving throw or the simian takes whatever the creature is holding in its hand and is now holding it with its tail. If the item is not tiny or have the light properties, then the item just drops to the ground.

Distract: the creature must make a DC 17 Dexterity saving throw or the simian distracts the creature by poking it in the eyes, pulling down their pants, tickling them, or something similar. The creature has disadvantage on attack rolls and skill checks until the start of the simian's next turn.

Nimble Feet: the simian can take the dash, disengage, or dodge action as a bonus action.

Shadow Step: if the simian is in dim light or darkness, they can teleport to another unoccupied place of dim light or darkness within 120 ft. They have advantage on their next melee attack roll before the end of this turn.

Kuzushi. Attacks against the simian while in dim light or darkness are at disadvantage unless the creature has something like blind sight or true sight. If a creatures misses a melee attack at the simian, then the simian can use its reaction to use their momentum against them. The attacking creature is either flung its full movement away from the simian or knocked prone 10 ft away from the simian.