Creating Zombie Ogres

Question

I'm currently trying to figure out the zombie creation mechanic for mt Pathfinder campaign. I'd like to bring back some ogres my players fought in a previous encounter as undead but I'm finding the instructions vague.

Hit Dice: Ogres have 4d8+12 for their HP and Zombification instructions say to drop their HD gained from class levels, but I don't think they have any. Do I just add two more HD for them being large creatures?

Armor Class: The Pathfinder section on Zombies just says to give them a natural armor bonus based on size (+3 for a large creature in this case) but the ogre already has a AC of 17 and an AC of 20 seems excessive for a zombie.

I'm sure I'm doing something wrong here, please help.

Answer 1

Hit Dice

Zombie's drop all Class HD, if existent, down to a minimum of 1 HD. Their new racial HD are d8. A general Ogre has no Class HD and will simply gain the 2 Zombie HD. Their HD were already d8, so no change in size. Their bonus HP is now determined by Charisma, which is set to 10.

Oddly, dropping their Constitution bonus and adding 2 HD (plus Toughness) actually nets neutral if you use average monster HP. They will still have 30 HP with Toughness.

Armor

Zombie Natural Armor replaces existing Natural Armor. Ref:

Armor Class: Natural armor is based on the zombie’s size:

Not "Increase Natural Armor" or "Gains Natural Armor that doesn't stack with existing", but "Natural Armor is..."

Statblock

A Zombie Ogre's statblock: (You'll notice, the CR actually drops)

Zombie Ogre CR 2
XP 600
NE Large undead
Init –2; Senses darkvision 60 ft., Perception +0
DEFENSE
AC 14, touch 7, flat-footed 14 (+4 armor, –2 Dex, +3 natural, –1 size)
hp 30 (6d8+6) [Note: Max = 54]
Fort +2, Ref +0, Will +5
DR 5/slashing; Immune undead traits
OFFENSE
Speed 30 ft. (40 ft. base)
Melee greatclub +9 (2d8+9) or slam +9 (1d8+9)
Ranged javelin +2 (1d8+6)
Space 10 ft.; Reach 10 ft. 
STATISTICS
Str 23, Dex 6, Con -, Int -, Wis 10, Cha 10
Base Atk +4; CMB +11; CMD 19
Feats Toughness
Special Qualities staggered 

You may have to update this if the party took the creatures' armor and weapons and they can't be replaced.

A comparison (see below) shows that you've traded in some armor (rotten flesh is mushy) for increased offensive abilities and some specialized defenses. In addition to having a larger effective health pool with DR/slashing, undead have a slew of immunities that can alter combat significantly. They have a higher CMB if they're commanded to use it, and deal slightly more damage with their greatclubs slightly more often. Of course, they're also constantly staggered meaning their primary mode of attack is the (so-called) "partial" charge.

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A typical Ogre statblock, for reference.

Ogre CR 3
XP 800
CE Large humanoid (giant)
Init –1; Senses darkvision 60 ft., low-light vision; Perception +5
DEFENSE
AC 17, touch 8, flat-footed 17 (+4 armor, –1 Dex, +5 natural, –1 size)
hp 30 (4d8+12) [Note: Max = 44]
Fort +6, Ref +0, Will +3
OFFENSE
Speed 30 ft. (40 ft. base)
Melee greatclub +7 (2d8+7)
Ranged javelin +1 (1d8+5)
Space 10 ft.; Reach 10 ft. 
STATISTICS
Str 21, Dex 8, Con 15, Int 6, Wis 10, Cha 7
Base Atk +3; CMB +9; CMD 18
Feats Iron Will, Toughness
Languages Giant 

Answer 2

The standard Ogre has no class levels

Do I just add two more HD for them being large creatures?

Yes, that's exactly it. Zombies are slow, but tough to kill. If the base creature has no character/npc class, you simply take their HD, convert to d12s and add whatever additional HD from the template based on their size. The standard Ogre from Bestiary 1 has no class levels.

But this doesn't mean that all ogres won't have a level in a class, they are intelligent enough to take class levels, and this is evidenced by all the Ogre variants who have class levels, such as the Ogre Brute.

You don't stack the armor bonus

but the ogre already has a AC of 17 and an AC of 20 seems excessive for a zombie.

Yes, but that's because you shouldn't add that natural AC on top of the base creature's AC, you gotta recalculate their AC, which will be reduced by their Dexterity penalty (-2, so they get a -1 to AC), and the template entry says the following:

It uses all the base creature’s statistics and special abilities except as noted here.

Since Armor Class is noted, you read that up and apply whatever says in there, which is:

Armor Class: Natural armor is based on the zombie’s size:

Well, since it's based on the zombie's size, the natural armor from the base creature can be scratched, it's irrelevant once the creature became a zombie.

This can be confirmed by looking at published zombified creatures, such as the Zombie Storm Giant (going from +12 to +4), or the Zombie Hill Giant (going from +9 to +3).

Example of creation

To make things simple, let's take a look at the Ogre's stats and then apply the zombie template on it. I won't go into detail about everything that has to be changed, but this should help you understand how the process goes.

The ability scores will be as follow (applying +2 Str, -2 Dex and null Con):

• Str 23, Dex 6, Con -, Int -, Wis 10, Cha 10

Now, let's take a look at the AC entry:

• AC 17, touch 8, flat-footed 17 (+4 armor, –1 Dex, +5 natural, –1 size)

This will be changed as follows: natural AC is now +3 instead of +5, and the Dex modifier is now -2 instead of -1. Which gives us:

• AC 14, touch 7, flat-footed 14 (+4 armor, –2 Dex, +3 natural, –1 size)

Also, notice that they also lose their Medium Armor Proficiency, so either take out that armor, or leave it there and apply the Armor Check Penalty to the creature's attacks, it's up to you. Personally, I would leave it there as it looks creepier.

Finally, another thing to note is that Ogres already have Toughness, so you don't add that hp to them again. Neither you calculate that based on their constitution score (now nonexistent), but on their charisma score. So their HP won't get that much of an increase, going from 30 (4d8+12) to 30 (6d8+6), despite the HD upgrade.

Answer 3

Hit Dice: Ogres don't have class Hit Dice, so just give them 2 more HD from being Large as you said. In addition, zombies use their Charisma modifier (of 10) to determine hit points instead of Constitution, so they'd have 6d8+6 hit points (6d8 base, +6 from Toughness, no ability bonus)

Armor Class: The ogre's +5 natural armor and the +3 natural armor it would gain from being a zombie don't stack, so its AC would stay 17.