Hi guys,
I'll start by saying that I'm not posting this to ask for basic balancing tips, as I've that down already. I can create encounters that are mathematically aimed towards a specific difficulty level, as long as they are creative but not insanely complex. Big action oriented guy, minions, multiple medium guys, spicy terrain, simple lair actions, sure.
Now, I love actual plays (D20 veteran), but how dahell do DMs like Brennan and Matt balance their insanely creative final bosses? This fights have VERY swingy terrain features that can straight up murder you, powerful lair actions, powerful spellcasters (a personal bane to balance i have no idea) AND change something basically every turn.
I really wouldn't know where to start to put down the actual numbers for anything here, there are so many variables opposed to a couple damage variables you can average to make a very educated guess on the actual difficulty it will pose.
These fights come up very swingy thanks to all these impediments, without really giving you the chance to average down any expected DPS by the party, and that's just to decide the enemies' HP...
How do you put the numbers down on sheets here?
The more creative the encounter is the more ways you have to adjust on the fly and the less CR is accurate. Sure it gives you an idea on which ballpark you are in.
For example you have multiple lair actions and a selection of those activate each round. If the PCs are hurting then you can choose a few soft ones to give then a chance to regroup and recover. If reinforcements are coming perhaps there are a few less. Similarly if the PCs are cruising, hit 'em hard.
Whether or not this crosses the border into DM fiat/fudging I'll leave up to you.
Also remember you don't have to use the highest DPR actions in general.
This is a good answer. DMs have a lot of dials to turn to adjust the difficulty of an encounter even just with how they play the enemies. Really I think there are few DMs who play enemies as deadly as possible all the time.
I know I'll sometimes play enemies more aggressively if the PCs are doing better in the fight, like attacking downed PCs or counterspelling healing. Whereas if they're struggling, I might find other things for the enemies to do that'll be a little less mean.
I mean, if there are downed PCs, they're struggling already, IMO.
Well, somewhat. With the way healing works in 5E it's pretty easy to get people back up, and you can often have one PC be downed and still have the rest of the party doing pretty well. If I'm running an enemy that wants to kill the entire party, and the party is trying to kill the enemy, having one at least person go unconscious is pretty common to make it actually feel challenging. But that doesn't necessarily mean that the party is actually in danger of losing the fight.