Bì-àn, the Guardian Dragon

Spell Warden. The Guardian Dragon's imposing presence hinders the power of spells within a 10-foot radius originating from it. Cantrips cast by creatures of its choosing that are within the radius, or that would pass into it, have no effect. When a creature tries to cast a spell of first level or higher within this radius, or passing into it, they must first succeed on a spellcasting check (DC 20 minus 4 times the spell's level), with the spell having no effect on a success.

Additionally, magical environments and terrain become nonmagical within this radius.

Iron Mind. The Guardian Dragon has advantage on Wisdom saving throws.

Guardian's Wrath. The Guardian Dragon makes one Rend attack, and can use Panopticon's Embrace.

Rend. Melee Weapon Attack: your spell attack modifier to hit, reach 10 ft., one target. Hit: 1d6 + 6 piercing damage.

Panopticon's Embrace. The dragon exhales subduing energy in a 30-foot cone. Each creature in that area must make a Wisdom saving throw (DC 15). On a failed save, a creature falls asleep for one minute, until they take damage, or until another creature takes an action to wake them up.