So, I have a player wanting to play a druid for this AP. Great! I love druids. She wants to have an orca as a companion. Again, great! A water based animal companion should go well with the aquatic nature of this AP.
Then I got to thinking. A fair amount of this campaign is submerged. Will an animal companion that needs to breathe air still flow well for this AP?
Are there better choices or suggestions?
Since orcas aren't actually classified as aquatic animals, but rather have the hold breath ability, it technically couldn't stay underwater for more than 2 hours at a time, approximately. That shouldn't be a problem except for the fourth book, which is almost entirely spent in an underwater city. As a gm, I'd highly recommend you give the payer some kind of cheap item that allows them to cast waterbreathing for a while on an animal or to give it permanently. Maybe something that only allows animals with Hold Breath to stay underwater for a full day/forever? As a GM, you have the possibility of making stuff up if you want. :)
What I'd be more worried about is the fact that most of this ap doesn't happen underwater. Is the player aware of that? What does she intend to do when her character needs to explore on land? I'd have suggested an amphibious companion, but I know only 3: the giant leech, the electric eel and the giant salamander. There are a lot of other animals with "hold breath" which at least have a land speed, though. Maybe that could become an in-between if the player wants something special to go in the water but doesn't want to leave the AC behind when exploring on land?
I understand the wish to try the aquatic options, since we don't get to see them often, if at all, but given the choice and the way animals with hold breath work, I'm not sure it is actually worthwhile. Maybe
Great feedback, I appreciate it. She's keen on the orca, which I think is fine. Like you said, I can make some buffs to help it along.
I may need to make some modifications to the AP to more make it more aquatic friendly.
Yeah. Searching again on the internet for solutions if she really wants an orca, I have been reminded of an item created for this AP that the players will get at level 4 or 5 if they don't skip the relevant encounter: the necklace of air adaptation. A lot of enemies at the beginning of book 2 have the item. I had completely overlooked it because none of my players have any water-reliance.
If you are willing to houserule that piscine animal companions have a neck slot or that the necklace can be transformed into a belt, and if you can give them some item to lengthen the "hold breath" ability of the orca by level 10, it could work.
Your player will only have to accept leaving her orca behind when they go inland during the first three levels, and it can at least help in the various coastal/boat encounters of that book.
One problem I see with this is that the early volumes of the AP spend most of the time on land. It isn't until the fourth book that underwater travel becomes really common. So your player needs to be ready to spend quite a bit of time without her companion.
But by the time underwater combat becomes more common you should have plenty of options to manage that enviroment. Your players will find a bottle of air for example, which should be sufficient to keep the companion going.