homebrew
Undead Fortitude. If damage reduces the seafallen 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 seafallen drops to 1 hit point instead. Weakly Armored. Whenever the seafallen takes more than 15 damage in a single turn, a piece of its coral armor chips off, reducing its AC by 1. This reduction is cumulative, but cannot reduce the seafallen's AC below 11.
Multiattack. The seafallen makes two anchor attacks. Anchor. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (1d12+5) 1d12+5 bludgeoning damage and the target must succeed on a DC 15 Strength saving throw or be knocked prone. If the creature was already prone, they are instead stunned until the end of their next turn on a failed save. Waterjet (Recharge 6). The seafallen releases a line of water in a 30-foot line that is 5 feet wide. Each creature in that line must make a DC 15 Dexterity saving throw. On a failure, a target takes 14 (4d6) 4d6 bludgeoning damage and, if it is Medium or smaller, is pushed up to 10 feet away from the seafallen and knocked prone. On a success, a target takes half damage and isn't pushed or knocked prone.
Environments. Aquatic, Coastal, Underwater