Chuul
Chuul in your setting include this cordyceps-twisted spawn: a Medium aberration that spreads fungal control through grappled prey.
Cordyceps-Infected Chuul Spawn
Amphibious. The chuul spawn can breathe air and water.
Cordyceps Infection. Once per day, the chuul spawn can attempt to infect a creature it has grappled with its cordyceps spores. The target must make a DC 12 Constitution saving throw or become infected. The infected creature takes 1d6 necrotic damage per round and is under the control of the chuul spawn. The creature can repeat the saving throw at the end of each of its turns, ending the effect on a success.
Grappler. The chuul spawn has advantage on attack rolls against any creature it has grappled.
Actions
Multiattack. The chuul spawn makes two claw attacks.
Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) slashing damage.