Geese = Gaggle
Frogs = Army
Eagles = Kettle
Rhinos = Crash
Starlings = Murmuration

I'm sure at least a few of these are utterly strange and unknown to a few of you but I thought it made a good transition into my topic. We have all these strange names for groups of animals but what about our dear mythical ones? Sure you can group werewolves in packs but I think some of the naturally more unique critters deserve something great. So if you all would like to help me name groups for the following that would be great (if you know of one that is preexisting that would be great too).

Dragons = Rage
Gryphons
Phoenixes Blaze
Unicorns = Joust
Bigfeet = Tromp
Dryads = Stand
Naiads = Rush
Leviathans/sea serpents = Rage/Twist
Cockatrice = Pierce

Feel free to add more to this group of groups if you want to find some names too!
Also, I don't know if I put this in the right spot but it seemed more like a cultural/language concept since it would be based a lot on what people know and see of them.

Phoenixes- Ashes.

Unicorns- Horns. They aren't that creative, but still!

Hm... That's not exactly what I meant... I mean, a Horn of Unicorns doesn't really make sense because there would be many horns... I could see something like "a rush of Naiads" though... See what I mean?

Alright. But like I said, I am not very creative with these things. Sorry.

Dragons: Flight. (That isn't original with me, by the way.)
Unicorns: Herd. (I'd use that for centaurs, too, or any other equine.)
Bigfoots ("bigFEET!"): Whatever you'd call a similar group of people.
Dryads (note that that's usually spelled with a "y"): Personally I'd just treat them as people, but "grove" might work if you want to use a different word.
Naiads (again, the usual spelling is slightly different than how you spelled it): Like dryads, I'd just use "crowd" or some other word for a group of people. I can't think of a word for a group of bodies of water; the best I can come up with is "school".
Leviathans/sea serpents: I imagine these as loners (by necessity if not by choice; rather like Abraham and Lot, any one part of the ocean can't sustain more than one of them), so I'd never have cause to describe a group of them.
Cockatrices: I'd look up what the word is for a group of snakes, and use that. But I don't use cockatrices.
No idea on gryphons (which I'd spell griffins) or phoenixes.

I edited in my choices so far. Also thanks to Seer for helping out!

@kingjon

Not all my dragons can fly. I needed something more unique for unicorns. Bigfeet are still animals so they hardly qualify as tribes. Sea serpents and leviathans are in groups at times.

I still think it should be a flight of gryphons and a blaze of phoenixes.

I'm still considering those. What about parch or sear? Do those work maybe?

A parch of phoenixes? A sear of phoenixes?

I think "Blaze" is the best word to describe a group of them, especially if you have a "rush" of naiads and a "joust" of unicorns.

My favorites are a "stand" of dryads and a "rage" of dragons. Those are great.

Thanks, I like those too. I'm trying to be a little unique with each one though. For example a knot of toads sounds oddly natural but really doesn't have a reason but a murder of crows is so called because they kill near dead things. I think Blaze seems a little too much along the same lines... This one is a hard one.

You might consider a Swallow of Sea Serpents... it just sorta sounds like it would fit them well.
On the same vein I came up with the idea of a Drop of Phoenixes.
As you can see I am fond of using verbs for groups.
Also, would you mind if I borrowed some your terms for myself in my stories? I particularly like your name of a group of dragons being a "rage."

Not at all, I don't even have all of these creatures in my world, I just wanted to name them. Now that I think of it, Leviathons are dragons anyway so a rage would be quite logical... especially if there happens to be an unfortunate fleet of ships nearby...