Help Understanding Pathfinder Hit Dice Advancement

[Seerow]

So I mentioned in another thread that I am likely going to be running a Pathfinder Adventure Path for my group in the not too distant future, as part of prep for that I am trying to get a handle on various aspects of Pathfinder I never bothered with looking into much. In this case, I have noticed several monsters indicated as an advanced version of a different monster, but with no statblock attached, just the new CR of the advanced creature.

So I am trying to get an idea of how Pathfinder handles hit dice advancement. Looking on the SRD, it seems like instead of having a set rate of HD per CR, it's more complicated and based instead on tuning the monster to a specific HP total, and figuring out how many hit dice you need to get there. The table provided also includes listings for HP/Attack Bonuses, but I am not sure if those are the bonuses that you use in place of what hit dice would normally grant, if they're what's expected, or if they're granted as part of the advancement on top of the normal stat increases.

Right now my understanding is:
Step 1) Figure out the new CR, and how much HP is gained getting to that CR.
Step 2) Figure out how many hit dice you need to hit that new HP total, more or less.
Step 3) If Hit Dice Increase > 50%, increase size category. Recalculate hit dice based on new con score for increased size, adjust hit dice gain accordingly.
Step 4) Apply other benefits of hit dice and size (increased stats, attack bonus, damage, saves, feats, etc)
Step 5) Apply additional bonus to hit, natural armor, and damage based on the monster advancement chart


But I am not sure this is right. Biggest points of confusion are on advancing to hit a target HP (do you try to get as close as possible without going over? as close as possible with leeway either way? Go to exactly the right HP amount and fudge effective HD rolls to make it happen?), and whether the step 5 is actually a bonus applied in addition to everything else, or is just what is expected to be gained. I would say it's expected, but AC especially isn't likely to go up, and damage isn't likely to jump the expected numbers outside of a size change.


Also can I just take a minute to marvel how Pathfinder managed to take the already fairly convoluted hit dice advancement from 3.5 and somehow make it even harder to understand?

[Psyren]

I don't know which AP you're reading, but generally when you see "advanced X" it means they simply slapped the Advanced Template onto X. Hence not reproducing the full statblock. Does that match with the CRs you're seeing?

[Seerow]

I don't know which AP you're reading, but generally when you see "advanced X" it means they simply slapped the Advanced Template onto X. Hence not reproducing the full statblock. Does that match with the CRs you're seeing?

Flipping through it (the AP in question was Kingmaker, which has a few different ones) it seems that yes they all do line up with a +1 CR, so that is probably what is going on. Thanks for pointing that out.


That said I am still interested in how Hit Dice advancement works, even if it is now mostly irrelevant, if only to sate my own curiosity. Or is it one of those things that everyone who plays pathfinder just agrees to stay away from?

[Grommen]

Flipping through it (the AP in question was Kingmaker, which has a few different ones) it seems that yes they all do line up with a +1 CR, so that is probably what is going on. Thanks for pointing that out.


That said I am still interested in how Hit Dice advancement works, even if it is now mostly irrelevant, if only to sate my own curiosity. Or is it one of those things that everyone who plays pathfinder just agrees to stay away from?

Just noticed that pathfinder also changed the type of dice used. For example outsiders in 3.5 used a D8. Under Pathfinder they use D10. Pretty much, in Pathfinder, if the BAB is full (IE. +1 per level/hit die) they will use a D10. Average BAB D8, and Poor BAB D6. Their are no D4 for hit points in Pathfinder.

In addition a lot of the undead, those that don't have a CON, use CHA for bonus hit points. They don't have D12 for hit points.

Toughness does not add 3 hp's total, it adds (for the most part) 1 per level/hit die.

Some of the NPC's might have more hit points than they should due to the Favored Class bonus (though I am not sure this applies to NPC's).

The CR for advancement is normally +1 CR for each HD. Unless it's undead with poor BAB, in that case I believe they get +1 CR for two Hit dice.

[Seerow]

Just noticed that pathfinder also changed the type of dice used. For example outsiders in 3.5 used a D8. Under Pathfinder they use D10. Pretty much, in Pathfinder, if the BAB is full (IE. +1 per level/hit die) they will use a D10. Average BAB D8, and Poor BAB D6. Their are no D4 for hit points in Pathfinder.

In addition a lot of the undead, those that don't have a CON, use CHA for bonus hit points. They don't have D12 for hit points.

Toughness does not add 3 hp's total, it adds (for the most part) 1 per level/hit die.

Some of the NPC's might have more hit points than they should due to the Favored Class bonus (though I am not sure this applies to NPC's).

The CR for advancement is normally +1 CR for each HD. Unless it's undead with poor BAB, in that case I believe they get +1 CR for two Hit dice.

That doesn't look at all like the monster advancement rules listed on the pfsrd (here: http://www.d20pfsrd.com/bestiary/rul...er-advancement). It doesn't say anything at all about 1 hd = 1 CR or anything along those lines, it's some confusing mess about "add hit dice until you gain this much HP, then do some other stuff and suddenly you magically have a new creature!".

What you describe sounds a lot closer to what I expected to find when I went looking, but doesn't seem to line up at all with what is written, unless there's a third completely separate monster advancement rule that I have managed to not find, and this page I keep referring to is some obscure thing that nobody talks about because it is insane?

[Psyren]

There are no hard rules around advancing monsters by HD, only guidelines. The main one to keep in mind is that it's like "building a monster from scratch" - i.e. it's an art, not a science, and sticking merely to numerical increases is not necessarily going to tell you what a final CR should be.

Step 3 is not only optional, invoking it could impact your application of step 2 (by changing the creature's Con, which gets them to the new hit point total more quickly.) And you forgot the all-important Step 6 - comparing the finished product to existing creatures of the new CR to assess reasonableness (as well as accounting for deviations the original creature may have possessed - above or below - relative to other creatures of its old CR.)

But again, the main point cannot be overstated - it's an art, not a science, so go with your gut more than what the math is telling you.