Annihilating Aura. Any creature that starts its turn within 30 feet of the nightmare must succeed on a DC 21 Constitution saving throw or take 14 ( 6d6 ) necrotic damage and grant the nightwalker advantage on attack rolls against it until the start of the creature's next turn. Undead are immune to this aura. Eidetic Learning. The nightmare can not be permanently killed so long as typhon organisms infest Luna Castellum. Each time it encounters the same group it will automatically have a single counter to the preys abilities. For example, facing a psi-user that needs sight to use his abilities, the nightmare will gain the blindness/deafness spell as an action. Or if an attacker uses radiant damage it will lose its vulnerability the next encounter and then gain resistance the following on so on. Life Eater. A creature reduced to 0 hit points from damage dealt by the nightmare dies and can't be revived by any means short of a wish spell. Instantaneous Movement. The nightmare can move through other creatures and objects as if they were difficult terrain. It takes 5 ( 1d10 ) force damage if it ends its turn inside an object. Its movement is more akin to a teleport than actual movement so it may pass through hostile creatures and attack from behind. Its movement never provokes attacks of opportunity. Psychic Mirror. If the nightmare takes psychic damage, each creature within 10 feet of the hulk takes that damage instead; the nightmare takes none of the damage. In addition, the hulk’s thoughts and location can’t be discerned by magic. Reactive. The nightmare can take 1 reaction at the end of each enemies turn. Turning Defiance. The nightmare and any other sword wraiths within 30 feet of it have advantage on saving throws against effects that turn Undead. Unusual Nature. The nightmare doesn’t require air, food, drink, or sleep.
Multiattack. The nightmare uses Ephialtes Slash twice, or it uses Ephialtes Slash and Finger of Doom, if available. Ephialtes Slash. Melee Weapon Attack: 1d20+12 to hit, reach 15 ft., one target. Hit: 28 ( 5d8+6 ) necrotic damage. The target must succeed on a DC 21 Constitution saving throw or its hit point maximum is reduced by an amount equal to the necrotic damage taken. This reduction lasts until the target finishes a long rest. Scream of Doom (Recharge 6). The nightwalker points at one creature it can see within 300 feet of it. The target must succeed on a DC 21 Wisdom saving throw or take 26 ( 4d12 ) necrotic damage and become frightened until the end of the nightwalker's next turn. While frightened in this way, the creature is also paralyzed. If a target's saving throw is successful, the target is immune to the nightmare's Finger of Doom for the next 24 hours.
Roll a 1d4 timer and tick the timer down each time the nightmare has a turn. If the timer is on 1 at the start of the nightmare's turn the following effect triggers: Arcane Enchantment. An orb appears on the battlefield of purple light. It shoots a coruscating line from its centre and begins spinning. These orbs persist until the end of the battle. The orbs impose a bane on attack rolls and saving throws. Any creature that fails a saving throw or attack roll takes 5 necrotic damage. Both the bane and the damage is cumulative. The timer has a -1 applied for each arcane enchantment active on the battlefield. A character can dispel a single enchantment using dispel magic or a rogue can disable one with a successful DC 14 Thieves Tool check. On a failure, the rogue takes 5 necrotic damage.
The nightmare can be encountered anywhere on Luna Castellum but only after multiple lesser typhoons have been killed by the party. Wherever it is encountered it will have some loot scattered in its "lair". Treasure should generally be themed to reflect the environment where possible:
Luna Castellum