Flying animal companion, recommended changes?

[TheInnsmouthLooker]

I've got a player who wanted to take a Roc animal companion in a previous game, and I was a little worried that it'd be too game-breaking with having to update every module to account for flight, so I disallowed it and said that I'd allow it in a more appropriate environment. I really don't have a problem with the Roc in general, but he's dead set on playing a Gnome Druid with a Roc companion in our upcoming LoF campaign. Will this be a major problem? I've read almost entirely through Howl of the Carrion King and I see a Peryton and Undrella, a Harpy, which really takes away the advantages of those enemies which I don't like. Would it be too much to add a second Harpy? What about in all the other combats? Certainly having a Roc scouting the town would speed up the time table for Kardswann finding out about the actions of the PCs. Should I add additional Gnolls to the Kulldis tribe with bows? I don't think that I'll allow the Roc to go underground or indoors unless it's incredibly spacious. Are there any specific encounters/locations that I haven't thought of?

[eakratz]

I think it will be fine. Sending out the roc to scout will be risky for the bird since if the peryton sees it it is going to go after it. Also, remember the geier from the monastery. A nice little medium sized bird would make a great meal for it. The gnolls should already have bows so any patrols or the ones at the gate might decide on target practice.

Unless the players are "kill first, ask questions never", chances are Undrella will become an ally not an enemy.

[Trench]

Our monk multiclassed into a sorcerer early on. It turns out that geier egg they found hatched and BOOM, instant vulture companion.