Modifying CR for Enlargement

[ByzantiumBhuka]

I've created an enemy for my players: a black dragon who has put research into making the Enlarge/Reduce spell permanent and has a bunch of supersized defenses.

However, I'm not quite sure how to calculate the encounter difficulty for these monsters. For example, I might normally put a garrison of a dozen orcs at the entrance to the lair, but if the dragon has cast Enlarge on them a few times, then they have 1. a few extra d4s on hits, and 2. increased size and weight as well as advantage on Strength checks, which increases their ability to grapple and drop boulders on the PCs.

So is there a good way to calculate the modified CR of creatures in this Dungeon of Enormity?

[Dark.Revenant]

You could recalculate their stat blocks as a creature one size larger, rather than using the spell effects verbatim. At the very least, this means a d8 (medium) hit die becomes d10 (large) or d12 (huge) and the creature's damage dice are magnified (1d8 becomes 2d8 then 3d8, etc). Strength should be adjusted upwards by ~4 per size increase, as should speed (+10 ft. at Huge) and reach (+5 ft. at Huge). You can adjust Constitution up by ~2 per size increase to increase the challenge. After this, you'd recalculate CR using the DMG methodology.

Some examples (note the standard Orc should probably be CR 1 instead of 1/2):

Big Orc
Large humanoid (orc), chaotic evil

Armor Class 13 (hide armor)
Hit Points 38 (4d10 + 16)
Speed 30 ft.



STR
DEX
CON
INT
WIS
CHA


20 (+5)
12 (+1)
18 (+4)
7 (-2)
11 (+0)
10 (+0)


Skills Intimidation +2
Senses darkvision 60 ft., passive Perception 10
Languages Common, Orc
Challenge 2 (450 XP)

Aggressive. As a bonus action, the big orc can move up to its speed toward a hostile creature that it can see.

Greataxe. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 18 (2d12 + 5) slashing damage.
Javelin. Melee or Ranged Weapon Attack: +7 to hit, reach 5 ft. or range 30/120 ft., one target. Hit: 12 (2d6 + 5) piercing damage.


Bigger Orc
Huge humanoid (orc), chaotic evil

Armor Class 13 (hide armor)
Hit Points 69 (6d12 + 30)
Speed 40 ft.



STR
DEX
CON
INT
WIS
CHA


24 (+7)
12 (+1)
20 (+5)
7 (-2)
11 (+0)
10 (+0)


Skills Intimidation +2
Senses darkvision 60 ft., passive Perception 10
Languages Common, Orc
Challenge 3 (700 XP)

Aggressive. As a bonus action, the bigger orc can move up to its speed toward a hostile creature that it can see.

Greataxe. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 26 (3d12 + 7) slashing damage.
Javelin. Melee or Ranged Weapon Attack: +9 to hit, reach 10 ft. or range 30/120 ft., one target. Hit: 17 (3d6 + 7) piercing damage.


If you go the spell route, you'll still have to recalculate CR; just apply the damage bonus to the stat block and calculate CR as per the DMG.

[Ninja_Prawn]

I would second the idea of just making new, giant versions of the monsters you want. It's cleaner, more flexible and more robust. And you players won't be able to whine "but but you can't stack the same spell effect twice, fnar fnar."

What I would suggest is to give them a few more hit dice than Dark.Revenant has. Especially if you want one big orc to replace a dozen regular ones...

And bear in mind, if you're used to running large mobs, that your action economy will suck now. The official encounter maths do take that into account somewhat, but it kind of sounds like you might not be sticking to by-the-book encounter building.