There aren’t too many gargantuan creatures in the Monster Manual. Ancient dragons grow to gargantuan size; aside from that, you’ve got your kraken, your tarrasque and your roc, a monstrous avian whose name, curiously, shares an etymology with “rook,” the chess piece (from Persian rukh, by way of Arabic) but not with “rook,” the corvid bird (from Old English, an imitation of its croaking call).
This terror with a 200-foot wingspan—roughly the size of a Boeing 747—hunts big, slow-moving game, snatching up an elk, a buffalo or even a giant as easily as a hawk or owl would seize a squirrel. It’s unaligned and has only bestial Intelligence. Its Strength and Constitution are extraordinary; its Dexterity, as ordinary as you can get.
Rocs are fearless. Aside from their enormous pool of hit points, they have proficiency in all of the big three saving throws (Dexterity, Constitution, Wisdom), plus Charisma. Magic doesn’t scare them, and it takes massive damage to even deter them: From their maximum of 248 hp, they’ll need to be reduced to 99 hp or fewer to be driven off.
Probably, the common folk’s fear of rocs is far greater than the threat they truly pose, because the average humanoid isn’t large enough to make much of a meal. If you see one diving toward your trade caravan, chances are it’s planning to carry off your team of horses, not you. A roc would have to be starving to bother to carry off an adventuring party.
Really, a roc has only one method of attack: its talon/beak Multiattack. A successful talon attack grapples and restrains its target, giving it advantage on a follow-up bite. Real-life birds of prey don’t try to carry their game off alive—they strike hard to stun it, or they grab it and tear open an artery so that it bleeds to death. So while it’s entertaining to think of a roc flying off with a moaning buffalo in its talons, the truth of the matter is, it’s going to try to finish off the buffalo first, then fly it back to its nest while it’s still fresh, or maybe even eat it on the spot. A roc does an average of 50 points of damage in a single round if both its attacks hit. That’s enough to do in a giant elk, or seriously injure an elephant.
As long as a roc holds a creature that isn’t dead yet in its talons, it will continue to attack that creature, and only that creature—unless it’s attacked itself. Then it will peck back at its attacker with its beak, without letting go of its prey. Or, if the prey is itself seriously injured (reduced to 40 percent or fewer of its maximum hit points), it will simply fly away with it, without regard for opportunity attacks. It has a base flying speed of 120 ft, so there’s no way any other creature is likely to catch up with it if it Dashes, short of casting wind walk.
And that’s basically it. Not all that exciting, but a reader asked for it, so I’m obliging.