Here is Gorth, the sub-boss:
GORTH - Cultist Priest (Paladin 2/ Cleric 5 (War Domain))
Medium humanoid (human), Chaotic Evil
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Armor Class: 21 (Plate, Shield, Defensive Style)
Hit Points: 48
Speed: 20 ft.
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Str: 13 Dex: 10 Con: 12 Int: 12 Wis: 14 Chr: 14
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Saves: Wisdom +5, Charisma +4
Skills: Insight+5, Intimidation +5, Medicine +5, Perception +5, Religion +4
Langs: Common, Elven, Infernal, Orc
Feats: Savage Attacker, War Caster
Challenge: 3 (700 XP)
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Channel Divinity (1/Day): Gorth can use his channel divinity to Turn Undead (Command Undead CR 1/2 or lower) or for his Guided Strike (grants +10 to attack roll, after roll but before outcome determined).
War Priest: As a bonus action, Gorth can make a second attack as part of an attack action. This ability is limited to two uses before a Long rest.
Lay On Hands: As an action, Gorth can heal up to 10 hit points of damage from a pool of healing power. This pool replenishes after a Long rest.
Divine Smite: Gorth can expend a 1st-level spell slot to deal an additional 2d8 points of radiant damage. Each additional level of the spell slot increases the damage by +1d8.
Spellcasting. Gorth is a 6th-level caster. Spell save is DC 13 and +5 to attack rolls with spells. Gorth has the following spells prepared:
Cantrips (at will):
Light, Resistance, Sacred Flame, Toll the Dead
1st Level (4 slots):
Command, Cure Wounds, Divine Favor, Healing Word, Inflict Wounds, Sanctuary, Shield of Faith, Thunderous Smite
2nd Level (3 slots):
Aid, Magic Weapon, Silence, Spiritual Weapon
3rd Level (3 slots):
Crusader's Mantle, Dispel Magic, Protection from Energy, Spirit Guardians
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Actions:
Mace (+1). Melee Weapon Attack: +6 to hit, reach 5 ft. one target. Hit: 5 (1d6+1) bludgeoning damage.
Savage Attacker. Once per turn, Gorth can re-roll damage for his mace and take either roll.
I think that is everything. The question is:
is Gorth a CR 3???
I don't want the encounter to be deadly at all. With a couple acolytes, and maybe a couple fighter-types (CR 1s), would this made a Moderate to Hard encounter (leaning more towards Moderate I think).
If I missed anything or messed it up,
please don't hesitate to bring it up!
I'll focus on your question about Gorth's CR for now... Tl;dr he's probably more like
CR 5.
Before I start, the attack/damage is wrong on his
Mace +1. It should be:
Mace +1. Melee Weapon Attack: +5 to hit, reach 5 ft., one target.
Hit: 5 (1d6+2) bludgeoning damage.
Also, for flavor purposes, I suggest changing his Divine Smite to dealing necrotic damage. Up to you.
Lastly, because you insist on presenting your NPC using PC rules, it makes CR calculation much more difficult. Why? Simple, because player-facing rules are more complicated with more to keep track of. Because DMs run more monsters, the DM-facing monster/NPC rules are simpler with less fiddly bits. Thus informed, let's dive in...
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Since monsters/NPCs typically don't usually have Feats, we need to evaluate how Savage Attacker and War Caster affect CR.
War Caster I'd treat as proficiency in the Constitution saving throw – thus, with 3 proficient saves that is a +2 effective AC when calculating Gorth's Defensive CR.
Savage Attacker is probably worth +1 damage since he fights with a d6 mace (I'm eyeballing, not running actual dice odds here).
Now we need to figure out Gorth's 3-round spell strategy. IME his maximum bang-for-his-buck will be
silence and/or
spirit guardians, possibly with
dispel magic if there's a golden opportunity. For CR calculation purposes, I'm going to assume he casts
spirit guardians on round#1, and it lasts till the end of round #2 (when his concentration gets broken).
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Let's start with his
Defensive CR. 48 HP starts us at CR 1/4. His AC is 21, but proficiency in 3 saves bumps that up to an effective AC of 23. That bumps his Defensive CR up to 4.
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What about his
Offensive CR?
Round #1! With
spirit guardians, I'd guess he'd catch 2 PCs on Round #1 and he'd be lucky to get 1 PC on Round #2 (but let's give him the benefit of the doubt), so that is 3 * 13.5 average damage = 40.5 damage over Rounds #1 and #2.
But he also gets a bonus action
mace+1 attack thanks to his War Priest trait, and I'm going to assume for these bonus action attacks he buffs them with Divine Smite using a 2nd-level spell slot, dealing 1d6+2+3d8 damage, which averages to 19, but remember his Savage Attacker feat, so that'll be about 20 damage.
So, 60.5 damage on Round #1.
On
Round #2, he attacks with his
mace +1 buffed with Divine Smite using a 3rd-level spell slot, dealing 1d6+2+4d8 damage, which averages to 23.5, but remember his Savage Attacker feat, so that'll be 24.5.
He also makes his bonus action attack with Divine Smite using a 2nd-level spell slot, for 20 damage.
So, 40.5 damage on Round #2.
Round #3 is the exact same as Round #2, so another 40.5 damage.
Thus, his
DPR over 3-rounds = (60.5 + 40.5 + 40.5) / 3 = 141.5 / 3 = 47 damage
That starts his Offensive CR at 7. His attack bonus +5 and his save DC of 13 mean I'd drop this down to CR 6. So it's Offensive CR 6.
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Thus,
Gorth's total CR = (4 + 6) / 2 = 10 / 2 =
5
As stated above, the CR system is not an exact science. There's a lot of art hidden in monster maths, and a different spell strategy or different targeting assumptions could change his CR by +/-2.
