Baron Nashor

Immovable Colossus. Baron has a long winding body that is rooted into the ground. He cannot be forcefully moved by any means. When moving, Baron always leaves melee range of whoever is around him, as he dives underground and emerges elsewhere.

Frightful Presence. Each creature of Baron's choice that sees him for the first time must succeed on a DC 17 Wisdom saving throw or become Frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Baron's Frightful Presence for the next 24 hours.

Legendary Resistance (3/Day): If Baron fails a saving throw, it can choose to succeed instead.

Multiattack. Baron can make 3 bite attacks, or 2 bite attacks and 1 acid attack. 1 bite attack may be replaced with tail pierce.

Bite. Melee Weapon Attack: +12 to hit, reach 5 ft., 1 target. Hit: 19 (2d10 + 7) piercing damage plus 5 (1d8) acid damage.

Tail Pierce. Ranged Weapon Attack: +12 to hit, range 40 ft., 1 target. Hit: 21 (3d8 + 7) piercing damage.

Acid Spit. Baron spits acid in either a 10 ft radius circle or a 20 ft line. Everyone in the area must make a DC 17 Constitution Saving Throw. On a fail, a creature takes 3d10 acid damage and has disadvantage on dexterity saving throws until the start of their next turn. On a success, they take half damage and gain no disadvantage on dexterity saving throws. The area counts as difficult terrain until the start of Baron's next turn.

Rear Guard. Baron unleashes spikes behind his back, damaging everyone within a 15 ft wide and 10 ft length area behind him. Everyone in that area must make a DC 17 Dexterity Saving Throw. On a fail, the creature takes 17 (2d10 + 7) piercing damage and becomes stunned until the end of their next turn. On a success, they only take half damage and don't have their movement speed halved.

Rear Guard. When Baron receives damage from behind him, he can activate his Read Guard attack as a reaction.

Baron can take 3 legendary actions, 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 dragon regains spent legendary actions at the start of its turn.

Detect. Baron makes a Wisdom (Perception) check.

Bite. Baron makes a Bite or Tail Pierce attack.

Acid Spit (Costs 2 Actions). Baron makes an Acid Spit attack.

Headbutt (Costs 2 Actions). Baron dives underground, moves up to half his burrowing speed, and then remerges. Anyone standing in the place where Baron emerges must make a DC 17 Dexterity Saving Throw, taking 2d6 + 7 bludgeoning damage and falling prone on a fail, or half as much on a successful one, as well as not falling prone.