Nian

Hold Breath. The nian can hold its breath for 30 minutes.

Trampling Charge. If the nian moves at least 20 feet straight toward a creature and then hits it with a gore attack on the same turn, that target must succeed on a DC 14 Strength saving throw or be knocked prone. If the target is prone, the nian can make one stomp attack against it as a bonus action.

Tremulous. The nian is inherently fearful of loud noises, fire, and the color red. It will not choose to move toward any red object or any fiery or burning materials. If presented forcefully with a red object, flame, or if it is dealt fire or thunder damage, the nian must succeed on a DC 13 Wisdom saving throw or become frightened until the end of its next turn. After it has been frightened by a specific red object or a particular source of noise (such as clanging a weapon on a shield) or fire (such as the burning hands spell), the nian can't be frightened by that same source again for 24 hours.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 17 (2d12 + 4) piercing damage.

Gore. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) piercing damage.

Stomp. Melee Weapon Attack: +6 to hit, reach 5 ft., one prone creature. Hit: 15 (2d10 + 4) bludgeoning damage.

Year's Termination (1/Day). The nian creates magical darkness and silence around it in a 15-foot-radius sphere that moves with it and spreads around corners. The dark silence lasts as long as the nian maintains concentration, up to 10 minutes (as if concentrating on a spell). The nian sees objects in the sphere in shades of gray. Darkvision can't penetrate the darkness, no natural light can illuminate it, no sound can be created within or pass through it, and any creature or object entirely inside the sphere of dark silence is immune to thunder damage. Creatures entirely inside the darkness are deafened and can't cast spells that include a verbal component. If any of the darkness overlaps with an area of light created by a spell of 2nd level or lower, the spell creating the light is destroyed.