Duergar Resilience. The duergar has advantage on saving throws against poison, spells, and illusions, as well as to resist being charmed or paralyzed.

Sunlight Sensitivity. While in sunlight, the duergar has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

KI points (14 / Rest, DC 18). You can spend these points to fuel various ki features. You start knowing three such features: Patient Defense, Step of the Wind and Stunning Strike (Con Save).
Flurry of Blows
- It must succeed on a Dexterity saving throw or be knocked prone.
- It must make a Strength saving throw. If it fails, you can push it up to 15 feet away from you.
- It can’t take reactions until the end of your next turn.

Evasion. Your instinctive agility lets you dodge out of the way of certain area effects, such as a blue dragon’s lightning breath or a fireball spell. When you are subjected to an effect that allows you to make a Dexterity saving throw to take only half damage, you instead take no damage if you succeed on the saving throw, and only half damage if you fail.

Stillness of Mind. You can use your action to end one effect on yourself that is causing you to be charmed or frightened.

Diamond Soul. Whenever you make a saving throw and fail, you can spend 1 ki point to reroll it and take the second result.

Multiattack. Rammos makes two Chain Spike attacks. If using a KI point, He makes four Chain Spike attacks.

Enlarge (Recharges after a Short or Long Rest). For 1 minute, the duergar magically increases in size, along with anything it is wearing or carrying. While enlarged, the duergar is Large, doubles its damage dice on Strength-based weapon attacks (included in the attacks), and makes Strength checks and Strength saving throws with advantage. If the duergar lacks the room to become Large, it attains the maximum size possible in the space available.

Chain Spike +1. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 11 (1d10 + 6) piercing damage, or 17 (2d10 + 6) piercing damage while enlarged. On a hit, the target must make a DC 18 Constitution saving throw or take 16 (4d8) thunder damage and be knocked prone.

Invisibility (Recharges after a Short or Long Rest). The duergar magically turns invisible until it attacks, casts a spell, or uses its Enlarge, or until its concentration is broken, up to 1 hour (as if concentrating on a spell). Any equipment the duergar wears or carries is invisible with it.

Wholeness of Body. You can regain 42 hit points. You must finish a long rest before you can use this feature again.

Deflect Missile. you can deflect or catch the missile when you are hit by a ranged weapon attack. When you do so, the damage you take from the attack is reduced by 1d10 + 19. If you reduce the damage to 0, you can catch the missile if it is small enough for you to hold in one hand and you have at least one hand free. If you catch a missile in this way, you can spend 1 ki point to make a ranged attack with the weapon or piece of ammunition you just caught, as part of the same reaction. You make this attack with proficiency, regardless of your weapon proficiencies, and the missile counts as a monk weapon for the attack, which has a normal range of 20 feet and a long range of 60 feet.