Ok, my scenario is that I want to create a Huge Snake, Constrictor. Now listed under the entry for Snake, Constrictor is given that you can advance the snake to 14HD which makes it Huge and CR 10.
The problem is when I go back to the advancement section and start doing the advancing the snake does truly strange things. I do the CR2 -> CR 10 table for AC Change and HP gain. The hp gain suggests that the snake should have 19 additional HD using the average hit point table to make that difference. Woah, that's 5 more than the listed amount in the entry. The HP difference was +110hp change and with the snake's adjusted CON of 20 (+5hp/HD) suddenly pushes the snake near CR 14 levels, not counting that the snake normally has the feat Toughness added to it.
The AC Changes along with stat adjusts push his AC to 27ish which is CR 12 range.
So if someone can please tell me what I'm doing wrong and if possible stat out the Huge Snake, Constrictor so that I can work it out in reverse that would be appreciated.
I do love what Paizo has done for D&D. I just want to make sure that when I need to advance a creature that I will do it correctly. Thanks in advance.
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How about you post your advanced snake's stat block? That might yield some clues.
In general (without going through the process of advancing the creature myself) it looks like you might be right that the CR is too low. The impression I get from the snake entry is that a simple "doubling" formula was used in writing its advancement suggestions (CR 2 » CR 5 » CR 10; 3 HD » 7 HD » 14 HD; Medium » Large » Huge).
Constrictor Snake CR 10
XP
N Huge animal
Init +7; Senses scent; Perception +19
Defense
AC 19, touch 11, flat-footed 16 (+3 Dex, +8 natural, -2 size)
hp 147 (14d8+84)
Fort +14, Ref +10, Will +7
Offense
Speed 20 ft., climb 20 ft., swim 20 ft.
Melee bite +19 (2d6+16 plus grab)
Special Attacks constrict (2d6+16)
Statistics
Str 33, Dex 16, Con 20, Int 1, Wis 12, Cha 2
Base Atk +10; CMB +23 (+27 grapple); CMD 34 (can’t be tripped)
Feats Skill Focus (Perception), Toughness, improved natural attack, improved natural armor, improved initiative, iron will, skill focus stealth
Skills Acrobatics +19, Climb +23, Perception +19, Stealth +18,
Swim +23; Racial Modifiers +4 Perception, +4 Stealth,
+8 Acrobatics
first applied table 2-2, page 296 to make it huge adjusted all the skills and other stats for size and new ability scores.
then increased HD, adjusting skill points, feat, ability scores (dex) and other stats.
I'll trust the CR 10 should be just about right, I didn't actually check it against other monsters.
You might want to increase te speed a bit, I think it should be 30' now, but it is a DM call.
Well it's not an exact science by any means but here goes.
Animal for the most part gets a size increase with each doubling of HD (give or take)
Medium Constrictor - 3HD-6HD
Large Constrictor - 7HD-13HD
Huge Constrictor - 14HD+
Animals have 4.5 HP per HD.
4.5 x 14 = 63 HP base
Base Con = 12 + 4 for size increase to Large + 4 to size Huge = 20 so 14HD x 5 = 70 HP from Con.
Toughness 14 HP
63+70+14= 147 HP
BAB for an animal is 3/4 so 14 HD is a BAB of +10
Str is 17 base + 8 for large + 8 for Huge or 33 or a +11 to attacks.
Dex is 17 base -2 for large -2 for huge or 13
Attack is 10 +11 Str - 2 Size
Natural Armor is 2 Base + 2 Large +3 Huge + 2 Improved Natural Armor
AC is 10 + 9 Natural + 1 dex - 2 Size = 18
Huge Snake gets 5 extra feats, a smattering of skills, and technically 3 stat bonuses of the DM's choosing. I'd personally bump strength +1 to get +1 to Damage and Con +2 to get an extra 14 HPs.
Increase damage dice on attacks and you are good to go.
Compare 14 HD vs the chart in appendix 1 of the bestiary and you'll see that a 14 HD animal is CR 9. Huge Snake has some special attacks so it gets bumped to a weak CR 10.
Or course you could copy-pasta from the SRD ;) even though their advancement has some errors (natural armor is wrong and no stat bonuses from HD).
Thanks for the examples, however I have one additional question. Why is the snake's AC so low? According to Table 1-1 the average AC should be around 24, the shown AC from the examples are showing a 5-6 point lower difference than that. The HP for the snake is about right, kinda moving into the CR 11 range but that's more a function of the toughness feat. Table 2-1 is indicating that between CR 2 -> CR 10 that the AC Change should be equivalent to +10. So should I be taking any additional AC changes such as the ones from size changes and subtracting them from that table to make the numbers appear more in line?
Once again thanks for the help, I'm slowly getting there :)
no, the table is just a guideline, the snake has low ac but essentially it is just a big snake. If it really comes up short in multiple areas and doesn't really make up for it you can either give it another HD and boost stats accordingly or lower it's CR by one.
Make sure you take the entire creature into account, and sometimes even how it will be encountered.
For instance it has a pretty good stealth ability, if you make an encounter in which it tries to sneak up on a lone PC it is MUCH more lethal,
if you plan it for a full party fight you might want to actually change some feats so it gets combat reflexes, vital strike is also a very good feat, I kinda went soft on it because it is a big snake, I do not want it to appear scarier than the villain they will encounter next.
Animals are basically big dumb brutes they've generally get HP/CR because they have higher HD/CR but they are relatively one-dimensional opponents with glaring weakness.
Having a swim speed and climb speed makes the snake a good ambusher in swamps but it's still basically something for the fighter-types to hack on.
This thing is awesoe for ambushing dumb players that go wondering off alone,or even better.. animal companions that are sent off to scout ^^
besides an 'awaken' spell can make it pretty interesting
If you are going with a Conan inspired Temple of Set analogue then the Fiendish Template would also be very appropriate. DR/10 good and SR 15 give it some more staying power if it can't pull off an ambush.