Monster CR

[BurgerBeast]

Suppose you have a monster with 60 Hit Points, 16 AC, and resistance to bludgeoning, piercing, and slashing weapons.

You calculate it’s CR using the DMG (275), expecting it to be about 4:

Hit Points 60, multiplied by 2 for the resistances (see table on DMG 277), gets you 120 Hit Points for DCR 4, which is modified to DCR 5 because of the AC.

You calculate the OCR and it’s 5.

Final CR 5. Proficiency adjustment from +2 to +3 is applied and doesn’t affect the OCR or final CR.

But... now if you figure out the DCR using the assumption that the monster's target CR is 5:

Hit Points 60, multiplied by 1.5 for resistances (see table on DMG 277), gets you DCR 2, which is modified to DCR 3 because of AC.

OCR is still 5.

Final CR 4. So now what? Remember dropping the Proficiency bonus to reflect the final CR will not reduce the OCR.

Is this monster CR 4 or CR 5?

Is there a general rule for how to go about "assuming a target CR?"

[pwykersotz]

Your question reminds me of this:

If you re-arrange the pieces of the upper "triangle" to form the lower "triangle", a square goes missing. Can you explain?
http://www.smart-kit.com/wp-content/uploads/2006/12/triangle%20puzzle.gif


I'm away from my books and unable to do a CR conversion right now, so I can't give a serious answer at the moment.

[Ashdate]

Well the triangle puzzle is solved once you realize the first image not actually a triangle!

I'm not sure if BurgerBeast's post is a question or a comment on the guesswork math behind 5e. But similar issues come up in monster creation because of the wacky shifting multipliers that occur when calculating the number of monsters.

But i find it more amusing to suggest that Burger has created Schrödinger's Monster: a creature that is simultaneously CR 4 and CR 5.

[FightStyles]

But i find it more amusing to suggest that Burger has created Schrödinger's Monster: a creature that is simultaneously CR 4 and CR 5.

This is awesome. However, it seems like it will need a new trait.

The Schrödinger Effect: The creature is both alive and dead. At the start of each player's turn, they may attempt to observe the creature using a WIS (Perception) check vs. a DC of 11. If they fail, the creature appears dead. Therefore, all attack automatically succeed but the creature does not suffer any damage. In addition, the creature doesn't suffer any conditions that would end if a creature were to fall unconscious (this does not effect any current conditions). If the check is successful, the creature appears alive and does not have any of these effects.

[XianTheCoder]

Your question reminds me of this:

If you re-arrange the pieces of the upper "triangle" to form the lower "triangle", a square goes missing. Can you explain?
http://www.smart-kit.com/wp-content/uploads/2006/12/triangle%20puzzle.gif

The slope of the Blue sub-triangle is 2/5, the slope of the red sub-triangle is 3/8... thus they don't actually create a large triangle when you place the hypotenuses together. The Blue triangle has a steeper slope than the Red triangle, meaning the area of the sub-triangle will be greater in the base. So... the 1 square gap is a result of the fact that the large "triangles" are not actually triangles, and the change in slope between the two smaller triangles that make up the length of the hypotenuse create different area measurements. :D

WHERE'S MY PRIZE??? I want the giant blue dog!

[supergoji18]

This illustrates what is in my opinion one of the major failings of 5th edition. In an attempt to "simplify" everything, the designers only ended up creating situations where there is even more confusion than if they had made something a bit more concrete.

[Mcdt2]

This is one of the biggest issues with the stupid way the DMG explains the perfectly serviceable math on CR calculation.

When you make a custom monster, the proper step 1 is to decide the EXACT CR the creature will be. Not what you "expect" it to be, what you know with 100% certainty its final CR will be. Ideally, you should also choose what the Offensive and Defensive CRs will be if they aren't identical.

Now, thanks to the table, we know what acceptable values we can give a creature based on the CR we have chosen. We also know how to adjust for slight variances (such as how much to reduce the average damage per round if we give them an overly high attack bonus). And since we now exactly what the final CR will be, we don't need to worry about using the wrong calculations for more complicated features such as resistances or traits.

The absolute last thing I usually decide is the actual ability scores and damage dice of attacks. If I know the CR gives a proficiency bonus of +4 and I need an attack bonus of +9, and I'm envisioning this creature to be dexterous, then it needs to have a Dex bonus of +5. If it then needs to do roughly 30 damage a round, then I know how to set up its attacks. If it makes 1 attack each round, it needs to deal ~25 dmg in dice, +5 for Dex. That could be 4d12+5 (avg 31 dmg), but it's odd to me for a Dex monster to have a single big attack. so maybe I give it multiattack, and give it three attacks dealing 1d8+5 (9.5 dmg each, total 28.5 per round).

Of course, you sometimes go back and tweak some small things. For example, if I assigned the above creature a low AC for its CR and high HP, that might be odd, especially if they end up with less than AC 15 (since with 20 Dex, you'd expect at least that much unless something is giving them a penalty). So maybe I adjust the AC back up to 15 and lower HP to compensate. Or maybe I don't and justify the discrepancy with a custom trait of some sort.

TL;DR: Decide whether or not you need a CR 4 monster right now, or if you need a CR 5 one. Then adjust the offensive and possibly defensive stats to match.