I've seen a few threads around about NPCs being a higher or lower CR based on equipment. I understand how to adjust the CR based on the equipment tables there. But what about monsters?
For example, if I have a cloud giant who is suddenly wearing +2 full plate and a ring of protection and a cloak of resistance. His AC and saves are through the roof compared to a normal one. How do I balance his CR to account for it?
As an example take a cloud giant vs a warden of wind. As presented in the AP, they are the same CR. But they certainly seem like they're a different difficulty!
I've found a nice rough rule of thumb useful. Drop CR by 1 with dropping everything by 1. Attack, damage and defences. And drop hit dice with 2.
This ofcourse with meleeing opponents.
I guess if you put, say, +2 weapon, +2 armor and one or two other useful items of similar power, you could rise the CR by 2.
I use the following.
Find the average value of the treasure the creature has.
Up to the value no change in CR
from 1 to 2 times the value add +1 CR
from 2 to 4 times the value add +2 CR
from 4 to 6 times the value add +3 CR
How many times have you had a random encounter of a giant the PCs kill it and the DM for fun allows the party to roll on the treasure table only to roll up a ring of protection and a cloak of resistance. Something that the giant would have been wearing?