So assuming that Brentai's plot summary remains mostly intact at this point, The Mayor will be undergoing a gubernatorial metamorphosis. Royam's "last" words have a haunting effect on Hizzoner, and he realizes he can no longer flee from his destiny. Thus he ascends the perilous Capitol Steps, to that ancient and shining-domed shrine of a greater power than municipal mortals were meant to know.
Perils await him therein unlike any he has encountered before. Lobbyists - themselves identical to an earlier, humbler boss - roam the halls in packs as a reminder of how much more powerful the party has grown.
Unconventionally laid out, the final room of the dungeon, the office of the soon-to-be-former Governor, is accessible from the get-go, where the incumbent can be spoken to, giving different messages based on the Mayor's progress through the capitol's obstacles. A harried but silver-tongued man is he, given to black humor. At first he treats the Mayor like a nobody, someone to be turned away diplomatically. Soon after that he condescends toward the Mayor as just another sucker who will perish on the campaign trail. Visits at around the two-thirds mark will induce the Governor to attempt to dissuade the Mayor from adopting his office, as it is a position that extracts a great price from the strongest of men. Finally the Governor realizes that it cannot be stopped; the ascendant Mayor is indeed worthy He pens a Letter of Resignation (which may or may not be useful later on), leaving the Mayor alone in the Governor's office, which will serve as his new base of operations.
As regards to the specific nature of the challenges, the Mayor must not only face the dangerous beasties (a few political, but most merely vicious - more on them below), but he must solve two puzzles: the first in the Legislature and the second in the Senate. In the Legislature, a bill is coming to a vote, and, if passed, it will be submitted to the Senate.
The Mayor must attach himself to the bill by pummeling the right legislator, who will propose that he be added as a rider. Certain clues (or perhaps block puzzles) will be present to indicate which is the right one, but it's perfectly possible to fight the wrong ones (they're identical, aside from elemental differences between the Majority and Opposition parties, and if he picks on on the bipartisan committee he has to fight two at once). The more of the wrong ones he fights, the more clues he will have, as they'll yield answers in response to beatings.
Once attached to the bill, he will be passed and taken to the Senate, where he has been called as a witness to the current Governor's impeachment. There will be a maze or find a key or something before he can answer the summons. Once there, he will be asked a series of plot-pertinent questions with Yes or No answers. The Speaker will invariably twist the answers negatively. Each question answered will result in starting with some sort of penalty - damage taken, a status affliction, or something. The correct answer is, of course, to Ignore all of the questions, leading to awkward silence and just making the hearing look bad. Regardless, when all the questions have been asked, the Senators will all pounce upon you, resulting in a boss fight, first against the Majority and Opposition Leaders (both of whom summon flunkies); when one of them goes down, he will be replaced by the Speaker, who has abilities affecting the order and frequency of attacks (equivalents of Haste, Slow, Stop, Delay, Quick, etc.) as well as to induce thematically appropriate status effects (silence, mainly).
Enemies fought in the Capitol include the aforementioned lobbyists and legislators, who (aside from the Senators) are the toughest common enemies in the area. There are the omnipresent hobos (who by this time have been palette-upgraded to Determined Panhandlers), naturally.
Also encountered are four varieties of lawbot. One of them is a floating security drone who will summon the other three. Red lawbots enforce the smoking ban, using abilities which diminish the party's Tophat. White lawbots enforce the weapon policies, using abilities which diminish the party's Cane. Blue lawbots enforce the sanctified peace and quiet of the government halls, using abilities which diminish the party's Monocle.
Also present, for some reason, are goblins, who always appear in pairs, always die if the other one dies, can only be affected by abilities that target multiple enemies, and have exactly opposite elemental resistances, which are different in every area; if one is vulnerable to a certain element, the other is healed by it, and vice versa.
There is a library in the Capitol, where one of the recurring minibosses may be found. I don't yet know what that miniboss might be. Maybe insufferable nerds?
This dungeon is obviously more person-oriented than most of the others will need to be, in terms of enemies. There can be arbitrary monster transformations if we want.
If there are any logical inconsistencies in that, I say we leave them in.