Young Cave Dragon

Darkness Shroud. The cave dragon naturally suppresses light near it. Bright light within 30 feet of the dragon becomes dim light, and dim light within 30 feet becomes nonmagical darkness. If this shroud overlaps bright light created by a spell of 2nd level or lower, the spell creating the light is dispelled.

Magical Tunneler. The cave dragon can burrow through nonmagical unworked earth and stone. While doing so, the dragon can choose whether to leave the material it moves through undisturbed or leave a 5-foot diameter tunnel in its wake.

Spiked Climb. The dragon uses its spikes to hold itself in place while climbing, allowing it to climb difficult surfaces, including upside down on ceilings, without needing to make an ability check. If it climbs upside down on a ceiling or suspends itself on a vertical surface while leaving its claws free, it can't use the Ruff Spikes reaction.

Multiattack. The dragon makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 7 (2d6) poison damage.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Poison Breath (Recharge 5-6). The dragon exhales a cone of black, poisonous gas in a 30-foot cone. Each creature in that area must make a DC 17 Constitution saving throw. On a failure, a creature takes 42 (12d6) poison damage and is poisoned for 1 minute. On a success, a creature takes half the damage and isn't poisoned. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Ruff Spikes. When a creature moves to a space within 5 feet of the cave dragon, the dragon flares its many feelers and spikes. The creature must succeed on a DC 17 Dexterity saving throw or take 4 (1d8) piercing damage and be prevented from entering that space.