In my game I'm about to introduce a group of Dwarf fighters that will start out friendly to the players but have a pretty good chance of becoming enemies of the PCs. I want them to be a fair amount stronger than the PCs (they are level 5) but not insanely so. I'm struggling to figure out what stats to give them to support that narrative.
After running this game for a while and throwing different combinations of monster CRs at them, I'm getting a decent feel for what is a challenging / deadly fight. They can handle a lot more than I first thought before I realized the difficulties were based on a 4-6 encounter adventuring day.
I've come across two main suggestions for building an NPC / monster like this.
take a monster stat block and customize.
create a PC
That led me to start comparing pc builds and monster stat blocks. Here it's suggested that an NPC with class levels has a CR equal to ~2/3 of its class levels. So I thought I'd build a 10th level fighter which should be about equivalent to a CR 7. That sounded about right to me. The party would need to work at taking down just one of these guys and a whole group would be completely out of the question.
So I build a level 10 fighter. I gave him splint armor and a shield
Str +4, Dex +0, Con +4, Int +0, Wis +1, Cha +0
a battleaxe +6 to hit thanks to dueling fighting style with 1d8+4 slashing damage. He'd get two attacks so that would average out to be (4+4) x 2=16 damage per round.
Compare that to the monster stats per CR on DMG pg 274. A CR 7 monster should have:
+6 attack bonus
45-50 damage per round
Ok, so 95 HP would be CR 2 / AC 13. The AC is off by 4. Per the guidelines, adjust the CR up 1 per every two AC difference. That's another 2 AC. Roughly 4 CR defensively. That seems a bit low. 4 CR vs the 7 CR I was going for.
16 damage / round is 2 CR.
2 CR goes with +3 attack bonus but this fighter has +6, a difference of three so I need to add 1.5ish CR. So that ends up being a CR 3 or 4.
Overall My level 10 fighter sounds like a pretty solid CR 4. Not what I was going for. Ok so maybe I just need to boost him up a bit to hit the suggested defensive and offensive stats of a CR 7.
+6 Attack bonus
45-50 dmg / round
Ok so +6 attack bonus matches up, good.
15 AC, meh, these guys are a bit better protected, no biggie.
161-175 HP, jeez.. that's quite a bit more HP, but maybe I'll boost it to 130 and split the difference with the AC.
This is where I'm really at a loss - 45-50 dmg / round.
How could a fighter put out that much damage?
Here I see that a Champion Fighter is only going to put out 17 dmg / round at level 10 and only 35 dmg / round at level 20. That doesn't seem right.
A level 20 fighter will only put out as much damage as a CR 5 monster?
I feel like I'm missing some pretty substantial understanding of these mechanics.