Undead Fortitude. If damage reduces the zombie chicken 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 zombie chicken drops to 1 hit point instead.

Beak. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage and the chicken attaches to the target and cannot detach. While attached in this way the target takes 2 (1d4) slashing damage at the start of each of its turns and the chicken moves with the target. After two rounds attached the zombie chicken shoots a smaller mouth on a tentacle from inside its beak. The mouth attaches onto the target area and a chicken egg pops through the mouth into the victim the victim then takes 2 (1d4) piercing damage and is infected with a disease - an egg. The wound then closes and the target regains 4 (1d8) hit points. A humanoid host can carry only one egg at a time. Over four weeks, the egg gestates, and forms an zombie chicken. After the egg is hatched, the host starts to feel unwell, its speed is halved, it has disadvantage on attack rolls, ability checks, and saving throws, and has its hit point maximum reduced by 8d10 every minute, as the chicken chews its way through vital organs until the host is dead. If the disease is cured before the egg hatches, the unborn chicken is disintegrated. Fiends, oozes, and undead are immune to the disease. When the target is dead a zombie chicken comes out of its chest and tries to escape, usually by killing everything nearby.