Advancing Monsters and CR

[Azazu]

I my experience as a DM I have had trouble with the CR of monsters that I have advanced.

This usually occurs with adding a lot of hit dice. I know that the MM says that doing this tends to screw up the CR.

But does anyone have any other guidlines to keep the CR in check.

What I notice is that the CR on advanced monsters usually is on the low side. Especially when templates are added.

Any advice would be great.

thanks

 

[Elder-Basilisk]

When you're done, do a sanity check. Take the monster you've created and compare it to other creatures of roughly the same type with the same CR.

For instance, I created a nearly max HD Anarchic Chimera for one of my modules. When I was done, I took a look at the chimera and compared it do a dragon at the same CR. More hit points, fewer attacks, better attack bonus, weaker breath weapon, weaker AC, no SR, but fast healing and more feats, etc. They seemed to be in the same ballpark. So I called it good. On the other hand, I took a look at a max HD Corrupted Chimera and decided it wasn't really a good idea. The ability to deal the amount of vile damage it would reliably deal per round wasn't balanced. So I scrapped that monster idea.

On the other side of the equation, I took a former town leader who had become an outlaw and was now on the run. Originally, he had been Com 4/War 1. Since he'd been on the run, I wanted him to pick up wilderness skills and favored enemy was perfect for him. So he became Com 4/War 1/Rgr 1. Ordinarily, that would make him CR 5. However, comparing him to a Ranger 5 or Warrior 6 makes it quite clear that he's not. With his +4 BAB and 4d4+2d8 HD, he's a lot closer to a Ranger or Warrior 4. Since he had some skills that he couldn't get as a CR 3 Warrior 4, I decided to assign him an ad-hoc CR of 4--the same as the 4th level ranger he resembles.

 

[dcollins]

I must admit, the rules as written for Hit Dice advancement don't seem to work so well.

What I do is go back to the guidelines in the "How to Create a Monster" article by Skip Williams (in Dragon magazine, on a later Dragon CD, I think on wizards.com someplace). Base CR there is thumbnailed at average hp divided by 15 (basically), then add for special abilities. I figure out the CR "bonus" on the base monster, calculate new monster base CR and add the same bonus. That usually works out much better than the official rule.