Gargantuan monstrosity, neutral
Armor Class 15 (natural armor)
Hit Points 315 (18d20 + 126)
Speed 20 ft., fly 120 ft.
Saving Throws Dex +7, Con +12, Wis +8, Cha +6
Skills Intimidation +6, Nature +6, Perception +8
Damage Resistances cold
Damage Immunities lightning, thunder
Condition Immunities exhaustion, frightened
Senses blindsight 60 ft., darkvision 120 ft., passive Perception 18
Languages understands Auran, Common, Druidic, Giant, and Primordial but can’t speak
Challenge 14 (11,500 XP)
Confer Lightning Resistance. The thunderbird can grant resistance to lightning damage to anyone riding it.
Illumination. The thunderbird sheds bright light in a 60-foot radius and dim light for an additional 60 feet.
Innate Spellcasting. The thunderbird’s innate spellcasting ability is Wisdom (spell save DC 18). The thunderbird can innately cast the following spells, requiring no material components:
At will: feather fall, fog cloud, gust of wind, thunderwave
3/day each: blindness/deafness (deafness only), call lightning, control weather, wind wall
1/day each: sleet storm, storm of vengeance
Keen Sight. The thunderbird has advantage on Wisdom (Perception) checks that rely on sight.
Legendary Resistance (3/Day). If the thunderbird fails a saving throw, it can choose to succeed instead.
Storm Aura. A creature that touches the thunderbird or hits it with a melee attack while within 5 feet of it takes 11 (2d10) lightning damage. The thunderbird can choose for its rider to not suffer this effect.
Multiattack. The thunderbird makes two attacks: one with its beak and one with its talons.
Beak. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 27 (4d8 + 9) piercing damage plus 11 (2d10) lightning damage.
Talons. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 23 (4d6 + 9) slashing damage plus 5 (1d10) lightning damage, and the target is grappled (escape DC 19). Until this grapple ends, the target is restrained, and the thunderbird can't use its talons on another target.
Lightning Strike (Recharge 5-6). The thunderbird hurls a magical lightning bolt at a point it can see within 500 feet of it. Each creature within 10 feet of that point must make a DC 20 Dexterity saving throw, taking 66 (12d10) lightning damage on a failed save, or half as much damage on a successful one.
Lightning Dash. The thunderbird can transform into a bolt of lightning. It then can use its movement up to its flying speed. If this movement triggers an opportunity attack, the attack is made at disadvantage. The thunderbird cannot use this ability again until it has finished a long/short rest.
The thunderbird 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 thunderbird regains spent legendary actions at the start of its turn.
Talons Attack. The thunderbird makes one talons attack.
Move. The thunderbird moves up to halve its speed.
Flash Bang (Cost 2 Actions). The thunderbird releases a blinding flash of light out from a 60-foot radius centered around itself. Each creature within the radius must succeed a DC 20 Constitution saving throw. On a failed save, a creature takes 18 (4d8) radiant damage plus 18 (4d8) thunder damage and is blinded for 1 minute. On a success, the target takes half as much damage and is not blinded.
||The battle raging scorned, with many wounds atorn, Bird of Thunder roared, against the Serpent Horned.
|—An excerpt from the Elvish poem The Bird of Thunder and the Horned Serpent.
Many fear rocs for their great size, and rightfully so. However, to say that they are the greatest birds of all is far from true: there is a creature imbued with power undeniably far beyond them. They are lightning, they bring rain where they fly, the wind is their blood, storms are their creation, and their wings are thunder. For those privileged enough to bear witness to them, the breath is stolen from their lungs as they view the flight of the thunderbird.
Bringers of the Rains. Thunderbirds are, in many respects, very similar to rocs: both are similar in size, appear as massive birds of prey, rest on mountain peaks, and have a taste for large animals. That is where the comparison ends, as thunderbirds are more powerful than any roc, which can be seen at even a passing glance. Their bodies are surrounded by an intercut dance of electricity and their eyes are crackling balls of lightning. When in flight, a thunderbird is surrounded by great, black thunderstorm that signals they’re near. They also wield a wide assortment of elemental magics, such as launching arcs of lightning, controlling weather patterns, and briefly transforming into bolts of lightning.
Thunderbirds carry an essence of nature itself. No one knows where they came from, but there’s a story for every side: scholars say that they come from the Elemental Plane of Air, while various clergies say that they were born of thunder gods. To the giants, they are creations of Annam, who created them to terrorize and punish them, and to druids, they are avatars of nature’s power. Part of the reason little is known about them is because they’re so rare; thunderbirds are seen so rarely that any knowledge an individual possesses is usually reserved to legends.
Kings of the Skies. Thunderbirds dominant the skies of almost any area they lair. They prey upon only the largest of creatures mostly, like elephants and giants, but deer will do when nothing else is available. The storm that surrounds the bird when it takes flight helps to disguise it from prey most of the time, though anything of humanoid level intelligence will usually take notice if a storm cloud suddenly changes direction without any wind.
Thunderbirds, however, are not without their opponents, but this often has little to do with competition as much as the establishment of dominance of the air. While they mostly respect any other creature as normal, thunderbirds will regularly attack large ocean creatures like whales, as they feel no such lower world creature should reach their size. Additionally, thunderbirds actively hunt down rocs, as they feel them to be too be shadows of what they are. Thunderbirds don’t even eat rocs when they kill them, as that would give them to much respect, so scholars postulate. The only other creature they treat this way are dragons; dragons and thunderbirds have been enemies as long as the two have known the other existed, and both will only stop fighting sharing their territory when the other dies. It is if only very partially, dragons that have kept thunderbirds from growing too numerous, as have thunderbirds for ancient dragons.
Druids venerate these creatures and any circles in the territory of one with flock toward them and die to protect them. These acts of worship and respect are almost never returned, however, as thunderbirds are much like much like Nature when it comes to humanoids; indifferent. Mostly they’re ignored by the massive birds, as they’re usually too small to be anything of interest. But also much like nature, when provoked a thunderbird will respond with nothing but pure wrath and fury. There are many a legend of thunderbirds, who have been scorned or otherwise violated, responding by attacking nearby settlements and even turning entire cities to smoldering rubble. However, with the right mixture of good circumstances and favor, thunderbirds can and will actively be benevolent guardians of the local people of the area. They will bring rain for their crops and lightning for those who would seek in any way to harm them.
A Thunderbird’s Lair
Thunderbirds dwell on mighty mountain peaks, whose points caress the sky. Here they make their nests, the only place can reside in relative peace. Here they look upon the world without inviting unwanted attention and rest in effective harmony.
- Lightning arcs, forming a 5-foot-wide line between two of the lair's solid surfaces that the thunderbird can see. They must be within 120 feet of the thunderbird and 120 feet of each other. Each creature in that line must succeed on a DC 15 Dexterity saving throw or take 10 (3d6) lightning damage.
- A strong wind blows around the thunderbird. Each creature within 60 feet of the thunderbird must succeed on a DC 15 Strength saving throw or be pushed 15 feet away from the thunderbird and knocked prone. Gases and vapors are dispersed by the wind, and unprotected flames are extinguished. Protected flames; such as lanterns, have a 50 percent chance of being extinguished.
- A thunderclap originates at a point the thunderbird can see within 120 feet of it. Each creature within a 20-foot radius centered on that point must make a DC 15 Constitution saving throw or take 5 (1d10) thunder damage and be deafened until the end of its next turn.
- Once per day, the thunderbird can alter the weather in a 6-mile radius centered on its lair. The thunderbird doesn't need to be outdoors; otherwise the effect is identical to the control weather spell. Unless the thunderbird has used this effect, rain becomes much more common within 6 miles of the lair, with thunderstorms raging within a 1-mile radius.
- Birds of prey within 1 mile of the lair act as the thunderbird’s eyes and ears. Deer and other large animals are strangely absent, hinting at the presence of a formidable predator.
- Ocean going creatures of significant sizes, such as whales or giant sharks, make themselves as scarcely seen as possible. The shores are lined with the corpses and bones of those that don’t, which are charred as though struck by lightning.
If the thunderbird dies, the effects fade over 1d10 days.