Two-Headed. The Roc has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, or knocked unconscious.

Penetrating Sight. The roc has advantage on Wisdom (Perception) checks that rely on sight and ignores dust, fog, or other materials which would heavily obscure an area. 

Flyby. The roc doesn't provoke opportunity attacks when it flies out of an enemy's reach.

Multiattack. The roc makes three attacks: two with its beak and one with its talons.

Beak. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 27 (4d8 + 9) piercing damage.

Talons. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 23 (4d6 + 9) slashing damage, and the target is grappled (escape DC 19). Until this grapple ends, the target is restrained. The roc can grabble two Large or smaller creatures in its talons but needs both claws for Huge and Gargantuan prey. 

The roc can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The roc regains spent legendary actions at the start of its turn.

Detect. The roc makes a Wisdom (Perception) check.

Wing Attack (Cost 2). The roc beats its wings. Each creature within 15 feet of the roc must succeed on a DC 22 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The roc can then fly up to half its flying speed.