Banehound (5e Creature)
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Medium aberration, neutral evil
Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 2) piercing damage. If the target is a creature, it must succeed on a DC 11 Constitution saving throw or take 2 (1d4) necrotic damage. The creature's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the banehound regains hit points equal to that amount.
Frightening Howl (Recharge 5-6). The banehound howls. Each creature within 30 feet of it that can hear it must succeed on a DC 11 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 banehound's Frightening Howl for the next 24 hours.
Horrors and Madness
Horrors on Ravnica are terror and madness personified. You can represent this reality by using the Madness rules in the Dungeon Master’s Guide.
Whenever a character fails a saving throw against the banehound's Frightening Howl, note that fact. At the end of the encounter, have each character who failed at least one of those saving throws make a DC 13 Wisdom saving throw. On a successful save, nothing happens. On a failed save, a character gains a form of Madness from the Dungeon Master’s Guide, with the severity depending on how many of the saving throws that character failed during the encounter. One to two failed saving throws result in a short-term madness, three failed saves results in a long-term madness, and four or more failed saves results in an indefinite madness.
Packs of wild hounds corrupted by either nightmarish aberrations called horrors or the dark magic of the Undercity. They have long been a part of the ecosystem of the Undercity hunting anything that has flesh and a pulse of life. Often roaming in packs of five to nine through the passageways, ruins, and streets of the Undercity. Often they will wait in low-lying areas, pits, or darken areas to ambush unaware creatures. Often howls of these beasts echo through the decaying, verdant spires of the Undercity chilling the spine of any who hear them as they call for the hunt.