First: total agreement on the "better adventure" aspect. Over in my story hour, incognito lured one of my players over here to read through the stuff and her first comment on the final round was "Good entry, Thomas... but, I kinda like Quickbeam's better".
She's a pretty finicky player, and that's pretty high praise.
So, exposition on ingredients first:
Brass Ring & Frenzy: I took BOTH bits of bait, naturally. Generally, kind of weak, but I do like how I mixed this ingredient with the frenzy. And incognito's snipe aside

, I like how I mixed it with the monk! Still, I can see how the ingredients were not seen as particularly strong.
Zoo: Monks have shown up in a LOT of IronDMs as an ingredient, in one form or another. And every time they have, the setting has morphed to include a monastery. Even QuickBeam's. Just once, I wanted something different... and so instead of a monastery, I got a zoo. Once I had the zoo, much of the rest of the plot resolved itself, including the Great White Hunter monk (taking a liberty with the "constantly testing oneself" description in the PHB) and the ranger with a conflict of interest (I shoulda had him in that IronDM home game instead of Muriel, long ago).
Hydra & Cycle of Life: As mentioned, the zoo fit everything together. Mouth just sort of popped out as a good monk target, and zoos are all about cycles of life.
Hidden Agenda: I'll quote myself here.
Note: I typically enjoy having very political situations, and most of my scenarios involve hidden agendas for someone. Heck, I hardly call something an agenda iffen it ain't hidden.
My first entry (Fool's Cold) was actually a better example of hidden agendas, with some agendas that could really bite the players in the butt. Even my second entry, as rotten as it was, had a hidden agenda! So I honestly considered this to be a weak use of the ingredient (somewhat deliberately - I rebelled by making the scenario itself fairly straightforward).
Single Combat: Yeah, weak, I know. It was more in how the monk viewed the situation, than in the actual situation

.
With that covered, designer's notes!
I knew as soon as I saw the ingredients that I wanted to write a straight-forward set of encounters/combats with maybe a chase scene... And I also knew that there would be no monastery. Call me a curmudgeon if you must

.
Since I didn't have any idea how to achieve that immediately, I went and read the flavor text for the monk and hydra, skimmed through the rings in the DMG for one that was made out of brass (answer:
ring of warmth), and generally killed time while my muse thought things through.
The first thing that jumped out at me was the fact that the hydra was neutral... an oddity, since it is so often presented as a MONSTER, yet here it is, a simple animal cursed with a healthy appetite. That gave me the idea for a zoo, and I immediately knew that, win or lose, I HAD to have a zoo where others would put a monastery.
So then I tried to figure out why a monk would be at a zoo, and the Great White Hunter with a Hidden Agenda was born. Cycle of Life just fit right in. The ranger just grew out of the interaction, and when I read back through for new hidden agendas, so did poisoning the food and the academy's hiring of adventurers... and then, as I was taking notes on hooks, I worked out hidden agendas the PCs might have.
I still needed a frenzy and a brass ring, and as I was staring at the two of them, and thinking about rings of warmth, my muse summoned up the city of brass, fire, rings, and the fact that the lernaean hydra has to be burned to be killed... the only way a monk is likely to kill a hydra by himself!
Once my
writing frenzy subsided, I worked on details of the zoo, fleshed out a few niggling details, and checked to make sure incognito wasn't going to nail me on divination/teleport spells a 7-8 level caster could throw.
Then I cut out about 500 words that weren't strictly necessary, and still ended up at 2000+.