Undead Fortitude. If damage reduces the Remembrancer Congregation to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the Remembrancer Congregation drops to 1 hit point instead.   Swarm. The Congregation can occupy another creature’s space and vice versa, and can move through any opening large enough for a Medium humanoid. The Congregation can’t regain hit points or gain temporary hit points.   Hungry Mob. If a creature ends their turn while inside the Congregation, they must succeed on a DC 12 Strength saving throw or be knocked prone. While knocked prone in this manner, the creature is considered grappled by the Congregation.   Nag'Hwil Mind. The Remembrancer Congregation is immune to any spell or ability which would control its actions, such as Charm Monster or a cleric's Turn Undead ability (though Destroy Undead could affect them).   Gestalt Will. A Remembrancer Congregation can telepathically control any undead with a CR lower than its own within 120ft., deciding their actions on their turn. Undead that do not share the Nag'Hwil Mind special ability may make a Wisdom saving throw (DR equal to 13+the Congregation's wisdom modifier) to resist this control; on a successful save, they are immune to the influence of any Congregation's Gestalt Will for 24 hours.   A Remembrancer which shares its space with the Congregation immediately becomes part of it, adding 13 (2d8+3) 2d8+3 hit points to both the current and maximum hit points of the Congregation and increasing its CR by 1/2.   For every 1 CR a Congregation gains, it gains 1 point of Intelligence and Wisdom, to a maximum of 20 for either. Depending on the CR of a Congregation, a DM may rule that it takes up a higher size category than Large. The actions, abilities, and proficiencies of a particularly high-CR Congregation are left to the DM's discretion.