Fowl Origin. The Goose Hydra can swim indefinitely on top of water, but can only stay submerged for 15 minutes at a time

Innately Disloyal. The Goose Hydra will accept as much food (especially bread) as some gives it, potentially eating infinitely, but it never becomes more loyal for being fed.

Wings. While walking on land, the Goose Hydra's dash action is worth 10 more feet of movement than normal, allowing a dashing Goose Hydra to move an additional 40 feet.

Multiple Heads. The Goose Hydra has 5 heads. These heads make individual saving throws against being blinded, deafened, frightened, stunned, and knocked unconscious.

Reactive Heads. For each head the Goose Hydra has beyond one, it gets an extra reaction that can be used only for opportunity attacks.

Wakeful. While the Goose Hydra sleeps, at least one of its heads will remain awake and alert

Venomous Cobra Chicken. The Goose Hydra's piercing damage also deals +5 acid damage

Multiattack. The Goose Hydra makes as many bite attacks as it has heads

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 6 (1d10) [piercing] damage.

Thunderous Honk. The Goose Hydra's heads can choose to thunderously honk. This has no mechanical effect, but is utterly terrifying. 

Dive Bomb. Recharge 5-6: While flying and taking the dash action, the Goose Hydra releases a dropping in a 10-foot wide circle on the area directly beneath it. Creatures struck by the dropping take 5d4+10 bludgeoning damage and 5d4+10 acid damage and are thoroughly grossed out for the rest of the day.