Young Black Dragon

Ambusher. When submerged in water, the dragon has advantage on Stealth checks. If the dragon hits a creature that can't see it with its bite, it can deal piercing damage and grapple the target simultaneously.

Amphibious. The dragon can breathe air and water.

Ruthless (1/Round). After scoring a critical hit on its turn, the dragon can immediately make one claw attack.

Innate Spellcasting. The dragons spellcasting ability is Charisma (save DC 14). It can innately cast the following spells, requiring no material components. 3/day each:fog cloud, pass without trace

Multiattack. The dragon attacks once with its bite and twice with its claws.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 20 (3d10 + 4) piercing damage plus 4 (1d8) acid damage. Instead of dealing piercing damage the dragon can grapple the target (escape DC 16) and a Medium or smaller creature grappled in this way is restrained. While grappling a creature the dragon can't bite another creature.

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) slashing damage.

Acid Breath (Recharge 5-6). The dragon exhales sizzling acid in a 40-foot-long 5-foot-wide line. Each creature in that area makes a DC 15 Dexterity saving throw taking 45 (10d8) acid damage on a failed save or half damage on a success. A creature that fails the save is blinded until the end of its next turn.