Legendary Resistance (2/Day). If the Young Elder Brain Dragon fails a saving throw, it may choose to succeed instead. Once it uses this feature, it can’t use it again until it finishes a long rest.

Siege Monster. The creature deals double damage to objects and structures.

Multiattack. The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage plus 4 (1d8) acid damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Tadpole Brine Breath (Recharge 5–6). The dragon exhales brinewater in a 30­-foot line that is 5 feet wide. Each creature in that line must make a DC 14 Dexterity saving throw, taking 49 (11d8) bludgeoning damage on a failed save, or no damage on a successful one. Any creature that fails this saving throw must make a DC 14 Intelligence saving throw, or be Charmed by the Young Elder Brain Dragon for 1 minute, turning into a Mind Flayer if Charmed for the entire duration. Any creature Charmed this way may make a DC 17 Wisdom saving throw upon taking damage; if they succeed, then they are no longer Charmed by the Young Elder Brain Dragon.

The Young Elder Brain Dragon can take 1 legendary action, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Young Elder Brain Dragon regains spent legendary actions at the start of its turn.

Tentacle (Costs 1 Action). Melee Weapon Attack: +6 to hit, reach 35 ft., one creature. Hit: 13 (2d8 + 4) bludgeoning damage, and the Young Elder Brain Dragon may choose if target is grappled (escape DC 16). Until this [Tooltip Not Found] ends, the creature is restrained, and the Young Elder Brain Dragon can't use its Tentacle attack.