Thinking it over, I'd prefer to see less Dwarf Mode mechanics at play in an Arena+ mode.
You could do it that way, surely, but the more overlap you have between modes, the less sense there is in having them be separate.
So things like:
resource and space intensive growers/cooks/brewers for fairly cheap,
Not so much a fan of that. Abstract that micro stuff from Dwarf Mode out.
ARENA MANAGER!
Yes plox.
I'd like gameplay to be about 25% managing funds, 50% arena design and strategy, and 25% team/gladiator managment.
I see it having two phases. In the first phase, you build. You spend your starting money, hire some combatants, ect... but don't have a lot of drains on your funds happening yet. When you're ready, you open the doors to the arena, and the fights you've set up take place. After the season is over, the arena shuts down, you make improvements and restock on supplies and fighters and the cycle repeats.
Managing Funds and ResourcesDwarf bucks (or whatever) would be used to buy new combatants, food for your combatants, gear and additional resources (Food, drink, trinkets and mementos to sell the crowd.)
Money is drawn from every dwarf that visits the arena. Dwarves that see a good fight (or an interesting/exotic fight) have good seats, eat good food and drink and have good mementos to buy leave the arena happy and eager to come back. Dwarves that don't get any or all of these things are less happy and less likely to come back. Personality of arena goers might come into play too.
You can set the ticket price yourself, or you can have the game automatically calculate what it thinks your ticket prices should be based on the size of your arena and other factors. A rough supply/demand model would be needed so you can make adjustments (like reducing ticket prices to drive up business) and tactical choices.
Employees would get paid and would drain funds, and combatants would drain food. Professional gladiators that you've hired would drain both, since they practically live there. I think employee hiring should also be automated, like employees just appear to fill vacant jobs, so again you don't get bogged down in the micro. They should still gain skill and make your arena better....but tracking every dwarf to the degree that Fortress mode does is overkill to me.
Food and drink would be purchasable off a menu, and you would be able to automate the process so you don't have to constantly check back. Food quality would impact both the health of your combatants and the happiness of the crowds.
Additional funds could be spent on things like better furnishings for the arena, advertisers and cryers to drum up business, or "celebrity" heroes drawn from the world file, that increase business when they make a "surprise" visit.
Arena Design and StrategyFirst the basics. Expanding your arena, like in Fortress mode, should be relatively easy and shouldn't cost you a lot of resources. The full array of traps, mechanics and such should also be there so we can make interesting/varied arenas. The amount of detail in the arena would affect "fight quality" which is how interesting/cool the spectators found the match.
You should be able to have more than one arena too. You could use the area designator to define a room as an arena, then set other variables for it like "main attraction" "specialty fight" "Do not clean this arena" "First-blood combat" (the match is over when someone draws blood) fight modes (Free-for-all, team bout, animal fight, mega-beast fight, ect...) and more.
Other area designations might be "vendor area" "bathrooms" "Petting zoo" (for the children) ect....
The placement of seating is critically important. You want spectators to be close, because getting a good view makes them happy. But you don't want them to get hurt by stray arrows, acid sprays, ect... Keeping traffic flowing through the stands and towards your vendors would also be important.
Improper arena design should consequences too. If you leave your arena open to the crowds, they might get involved. Or your prison combatants might try to escape, or the fight might spill out into the stands and result in a lot of spectators leaving wounded and very unhappy. Clogged thoroughfares should mean that spectators don't get to see the fight, buy things or even use the bathroom before they leave the arena, which in the end results in less profit and return customers for you.
Team/Gladiator ManagementCombatants are either professionals, animals or unfortunates. Animals are bought from caravans, unfortunates from slave traders and professionals are contracted.
Initially, you should only be able to afford criminals, slaves, prisoners of war and common (but dangerous) animals like wolves, boars, ect.... The unfortunates would be low quality to average skilled combatants that don't make for a really exciting match. They would need to eat (as would the beasts), although not a lot, and you could feed them low quality food to keep cost down. They won't be particularly healthy or eager to fight though, and will give a poorer show because of it though.
The amount of enjoyment spectators get out of a fight is based on:
The quality/skill/rarity/numbers of the fighters involved.
The disparity between combatants (10 peasants versus 5 legendary champions is not an interesting fight.)
The size, detail and complexity of the arena.
The deadliness of the fights (First blood vs. to the death, wooden weapons vs. steel weapons)
The body/injury count at the end of the fight.
The mode of the fight (Animal fights being the least interesting, then free-for-alls, then team bouts, then mega-beast fights.)
Better equipment can keep your combatants alive longer, but they can also increase lethality. And while weaker weapons keep your combatants alive longer, the crowds aren't stupid. They know those are wooden swords. So they don't get as much out of the fight. And while your veteran gladiators draw more crowds, they kill more people too, unless you put them in non-lethal/first-blood fights...but then you might be under using your resources.
Arena SurgeonAs an addendum to gladiator management, you could hire a surgeon. Since the Hospital is part of the next Fortress update, the framework is pretty much done. Again, I'd suggest abstracting some of it to keep the scope of Arena mode focused. A surgeon would be an off-screen menu where you could view the injuries/status of wounded combatants. A surgeon could improve (or worsen!) a fighter's chance of recovery, stave off infection, reduce recovery times, and on.
An animal trainer/caretaker that does the same thing for beasts might also be appropriate.
Mega-beastsMega-beasts would represent the ultimate Arena fight. They''d be prohibitively expensive to acquire, and unlike other fighters, would require you actually build a pen to hold them and get them into the arena. Doing this improperly would result in a mega-beast rampaging through your arena on or off-season, and is the one thing other than economic decline that could utterly ruin your arena.
But the pay off would be huge. People would come from all over the world to see your mega-beast fight groups of combatants, a crack squad of legendary gladiators or even another mega-beast, and guarantee you at least one season of strong return business.