Keen Sight. The roc has advantage on Wisdom (Perception) checks that rely on sight.

Caustic essence. This roc is of a bloodline whose ancestor's eggs were breathed upon by a black dragon. All melee attacks this roc makes deal additional acid damage. 

Multiattack. The roc makes two attacks: one 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 and 2d8 acid damage

Talons. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 23 (4d6 + 9) slashing damage and 2d6 acid damage, and the target is grappled (escape DC 19). Until this grapple ends, the target is restrained, and the roc can't use its talons on another target. At the start of the roc's turn, any grappled target takes an additional 2d6 acid damage, and suffers a -1 penalty to the AC of any armor they are wearing.