The Big Smackdown. The End Of The Season-Slash-World.
The dénouement of the season is, as a rule, pretty heavy on the fight scene.
This is for the title, so make it big. Failure will lead to an apocalypse and possibly cancellation of the show.
Of course, Buffy being as weighted in favour of its heroes as it is, this isn't really a concern. Individual characters may fall, if it's dramatically appropriate. Generally, however, evil is going to have its ass kicked and it's all about how.
I don't like to restrict the narrative-y flow of fight scenes with maps, but sometimes the tactics get involved enough that it's necessary and this may be one of those times. And if not, then do have some interesting environmental features to throw in, like a collapsing building, shafts of sunlight when fighting the king of all vampires, a horde of zombies in the way, anything that either side can use to their advantage.
But while the monster mash is the main focus, if this isn't a one-session double feature with the Build-Up there may still be time for making plans, joking about the failure to make plans, resolving character plots, pointing out the lack of resolution in character plots, foretastes of next season, last-chance sex, gloating by the Big Bad, extra gratuitous violence like clobbering an underworld contact or casually staking a vampire on the way to the main event... That kind of thing.
Example: Rock Hard
The city is slightly in ruins and the Siren now commands a giant sea monster planning to eat everybody.
Fighting her will involve getting into the ruined, still-quaking arena, or chasing her through the cracking, flooding streets and over collapsing rooftops to get high enough.
Are we gonna let this go?
I don't think so.