Huge monstrosity (mount), neutral evil

Armor Class 15 (natural armor)
Hit Points 84 (8d10 + 40)
Speed 60 ft.

19 (+4) 16 (+3) 20 (+5) 7 (-2) 14 (+2) 10 (+0)

Skills Perception +4, Stealth +5, Survival +4
Senses darkvision 60 ft., passive Perception 14
Languages Understands Sylvan but can’t speak
Proficiency Bonus +2
Challenge 4 (1,100 XP)


  • Charge. If the sianach moves at least 20 feet straight toward a target and then hits it with a ram attack on the same turn, the target takes an extra 7 (2d6) damage. If the target is a creature, it must succeed on a DC 14 Strength saving throw or be knocked prone.
  • Rampage. When the sianach reduces a creature to 0 hit points with a melee attack on its turn, the sianach can take a bonus action to move up to half its speed and make a bite attack.
  • Saddle. The sianach can wear a saddle on its back. One Large, two Medium, or four Small creatures can sit on the saddle without squeezing. To make a melee attack against a target within 5 feet of the sianach, they must use spears or weapons with reach. If the sianach dies, creatures hanging fall straight down, taking falling damage, and land in unoccupied spaces within 5 feet of the sianach’s position on the ground.
  • Sure-Footed. The sianach has advantage on Strength and Dexterity saving throws made against effects that would knock it prone.


  • Ram. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage.
  • Hooves. Melee Weapon Attack: +6 to hit, reach 5 ft., one prone creature. Hit: 22 (4d8 + 4) bludgeoning damage.
  • Bite. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 9 (1d10 + 4) piercing damage.
  • Frightening Screech (Recharge 5-6). The sianach screeches. Each creature within 30 feet of it that can hear it must succeed on a DC 12 Wisdom saving throw or be frightened of it for 1 minute. The frightened 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 the sianach’s Frightening Screech for the next 24 hours.


The monster stag is a towering and fearsome creature, a dark fusion of a majestic stag and the embodiment of primal forces. Its body is immense, standing about ten feet tall at the shoulders and stretching over 15 feet in length. Its coat is a deep, earthy brown, mottled with patches of moss and lichen that seem to grow naturally upon its hide. Enormous antlers, resembling gnarled and twisted branches, crown its head, each one adorned with sharp, jutting points.

The sianach (SHE-an-NAKH), also known as the Monster Stag, is a creature of dark forests and fields, particularly in mountainous regions. It is a massive and aggressive deer-like monster that instills fear into those who encounter it. Sianach are often associated with hags, serving as their mounts and companions.

Sianach are fierce predators and meat eaters, a stark contrast to their herbivorous relatives. They are known to hunt hunters of elk and other creatures, tearing them apart and consuming their remains. With their green glowing eyes and hooves, they strike terror into the hearts of those who see them. Sianach are known for their powerful charge attack, ramming into their prey with tremendous force.

Hags adorn sianach antlers with ritualistic relics, runes, skulls, and other magical objects to enhance the creature’s abilities or grant it magical powers. Each sianach has different decorations in its antlers, conferring unique powers.

Section 15: Copyright Notice

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

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