As you might guess, I prefer Single-digit Monsters to charts. I also like simple math formulas, as long as they are easy to use and remember (there are few number you have to remember here, other than the number 3).
How would that work in 5e?
The DM's Guide gives you the numbers, but not the formula. Fortunately, it is not hard to find a few patterns. The results are very, very close to the actual table, but if your monster doesn't match this exact numbers, remember that the DMG tells you not to worry about this a bazillion times.
So hee is a generic stat block, and some explanations to go with it.
The Generic Stat Block (CR 1-20)
AC: 13 + CR/3* (maximum 19)
Save DC: 13 + CR/3.
HP: 15 x (CR+4)
Attack bonus / skills: 3 + CR/3**.
Damage: 1d10 + 1d10*CR (for melee attacks).
# attacks: 1 + CR/6 (total damage is unaffected).
*Always round down.
** Alternatively, 4 + CR/3 if CR>3.
|Click HERE for the PDF.|
AC, Attack bonus, STs, Good skills and Save DCs: magic number THREE
Start with +3 to attack bonus, skills, saves, etc., and 13 to AC and Save DCs.
Add one third of CR on top of that (round DOWN). Maximum AC is 19.
If you want to be really faithful to the DMG's table, you should add +1 attack bonus for CRs greater than 3 ("adjusted" column).
The same number you use for attack bonuses can be used for everything the creature should be good at; some skills, a couple of saving throws, etc. You can use a Fortitude / Reflex / Will mindset for that if you want, or just use common sense,
The table below is for comparison only; the whole idea is that you shouldn't need a table in the first place.
|AC/Save DC*||Attack Bonus, skills**, etc|
*Maximum AC is 19. Otherwise, the difference between AC/DC is negligible.
** 5e has no formula for skills.
Weak skills (CR/5)
In 5e, a powerful PCs and monsters might have NO bonuses when dealing with their weak spots. A level 20 Fighter might have a +0 bonus to Intelligence saves or Nature checks, for example. On the other hand, as the number of class features, ability scores improvements and feats increase, the character has a greater chance of having SOME way of dealing with these dangers.
There are no easy solution for this. Of course, weak skills and saves should be weaker than strong skills and saves. Dividing the CR by FIVE seems to put thing in the right ballpark for me, but eyeballing it might be just as good.
Damage output: the rule of SIX, and playing around with d10s
As you can see in the DMG's table, from CR 1 to 20 monster's get +6 damage per CR. Starting damage is also close to 6. Average damage, therefore, is close to 6+(6xCR).
This makes it easy to play around with dice. You can start with 1d10 plus 1d10 times CR. 1d12 would work too, but 1d10 gives me more wiggle room. Then you change the size of the dice for special attacks.
For example, let us say we have start with a CR 5 monster - 6d10 damage per round. If the attack affects two or three nearby targets at once, use 6d6 instead. A ranged attack might cause 6d6 damage, and so on. Use the 6d12 for a special attack such as a breath weapon that affects multiple characters and causes half damage on a successful save, but has another built-in limitation, such as a 5-6 recharge or 3 uses per day.
Give monsters a number of extra attacks equal to their CR divided by SIX, round down, without adding more damage. For example, a CR 12 monster causes 13d10 damage divide in three different attacks; maybe two 4d10 claws and one 5d10 bite, etc.
Monsters HP is close enough to 15 times (CR+4) that you can also play with this numbers. If the monster has various resistances and immunities, for example, you can reduce its HP to 10x(CR+4). The same applies for high ACs, invisibility, teleportation, and so on.
Beyond CR 20: another rule of three
For CRs greater than 20, each increase in CR TRIPLES the extra damage and HP. Instead of +6 damage and +15 HP, monsters get something close to +18 damage and +45 HP. But, at this point, it might be easier to just check the table. Also, it is a bit unlikely that one will create a CR 30 monster on the fly...
For CRs lower than one, there is no exact formula, but you can just multiply 120 HP and 16 damage for the CR (i.e,. CR 1/8 has 15 HP and causes 2 points of damage per round) to find something roughly compatible.
Click HERE for the PDF.
Click HERE for the PDF.