Dragon, Beithir

Family: Dragons

Huge dragon, unaligned

Armor Class 17 (natural armor)
Hit Points 178 (17d12 + 68)
Speed 40 ft., climb 40 ft., swim 40 ft.

21 (+5) 14 (+2) 18 (+4) 7 (-2) 12 (+1) 9 (-1)

Skills Perception +5, Stealth +6
Damage Immunities lightning, poison, thunder
Condition Immunities poisoned
Senses darkvision 90 ft., passive Perception 15
Proficiency Bonus +4
Challenge 12 (8,400 XP)


  • Amplify Lightning. Whenever a spell that deals lightning damage includes one or more beithirs in its area, the spell deals an extra 9 (2d8) lightning damage.
  • Lightning Absorption. Whenever the beithir is subjected to lightning damage, it takes no damage and instead regains a number of hit points equal to the lightning damage dealt.
  • Regeneration. The beithir regains 10 hit points at the start of its turn. If it takes acid or bludgeoning damage, this trait doesn’t function at the start of the beithir s next turn. The beithir dies only if it starts its turn with 0 hit points and doesn’t regenerate.


  • Multiattack. The beithir makes two attacks: one with its Bite and one to Constrict or Sting.
  • Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 21 (3d10 + 5) piercing damage plus 5 (1d10) lightning damage.
  • Constrict. Melee Weapon Attack: +9 to hit, reach 5 ft., one Large or smaller creature. Hit: 16 (2d10 + 5) bludgeoning damage. The target is grappled (escape DC 17) if the beithir isn’t already constricting a creature, and the target is restrained until this grapple ends.
  • Stinger. Melee Weapon Attack: +9 to hit, reach 20 ft., one creature. Hit: 10 (2d4 + 5) piercing damage, and the target must succeed on a DC 16 Constitution saving throw or take 13 (2d12) poison damage and become poisoned until it finishes a short or long rest. The target’s hit point maximum is reduced by an amount equal to half the poison damage taken. This reduction lasts until the poisoned condition is removed or the target fully immerses itself in the nearest body of water before the beithir does. The target dies if its hit point maximum is reduced to 0. Lightning Jolt (Recharge 5 6). One creature the beithir touches within 10 feet of it outside water, or each creature within 30 feet of it in a body of water, must make a DC 16 Constitution saving throw. On failed save, a target takes 13 (3d8) lightning damage. If the target takes any of this damage, the target is stunned until the end of the beithir’s next turn. On a successful save, a target takes half as much damage and isn’t stunned.


The beithir is a fearsome serpent-like creature, resembling a large snake with shimmering scales in varying shades of green and blue. Its sinewy body measures approximately 20 feet in length, and it moves with a graceful slithering motion. The beithir’s head is adorned with sharp fangs and piercing eyes that exude an otherworldly glow.

The beithir is known to dwell in mountainous caves, valleys, and rugged terrains. It prefers regions associated with thunderstorms and electrical activity, drawn to places where the power of lightning and thunder is most potent. It often makes its lair deep within caverns or alcoves within rocky cliffs.

The beithir is deeply connected to the elemental forces of lightning and thunder. It possesses innate resistance to lightning and thunder damage, reflecting its affinity and adaptation to these natural energies. The beithir’s venomous sting injects a potent toxin into its victims, causing additional poison damage and debilitating effects.

The beithir is a cunning predator, utilizing its serpentine agility and climbing abilities to stalk and ambush its prey. It strikes swiftly and silently, using its powerful bite and venomous sting to incapacitate its targets. The beithir’s lightning aura crackles with electrical energy, damaging nearby foes and adding an element of terror to its attacks. It relies on its frightful presence and terrifying roar to disorient and intimidate its prey, making them more vulnerable to its lethal strikes. Once its prey is subdued, the beithir devours it whole, ensuring its own survival in the untamed wilderness.

Beithirs are notoriously hard to kill. They are known to regenerate from just the head, with the only means of truly eliminating them to sever the head and then bash the skull to bits.

Section 15: Copyright Notice

5E RPG: Celtic Bestiary. Copyright 2023, Mal and Tal Enterprises, LLC; Author Michael Tresca.

This is not the complete section 15 entry - see the full license for this page