Help determining the CR of a "doppelganger" encounter

Question

I'm creating the final encounter in a magical tower. When the party enters the room, an exact copy of the members appear in the center of the room.

Everything will be exactly the same, what spells are prepared/used, special abilities per day, active buffs, what items, how many uses, etc... down the line.

What would be the CR for this encounter?

(The party composition isn’t known at the moment. But it is shaping up to be around a level 11 game. One is a sorcerer, and one is a wizard. Don’t know if there will be more players besides that.)

Answer 1

CR 101

Generally, the CR of any Class Level NPC is the same as its level minus 1.

So the CR of a 10th level NPC Fighter is 9. The CR of a 10th level NPC Wizard is also 9.

CR increases differently when adding multiple creatures. Two CR 9 creatures are not CR 18, It's 11. Counting from 2 to 6 (the typical party sizes):

• Creatures: 2 CR: 11
• Creatures: 3 CR: 12
• Creatures: 4 CR: 13
• Creatures: 5 CR: 14
• Creatures: 6 CR: 14 (no, that's not a typo. I'll explain later)

CR calculation is a complex business and you can read all about it here. I'm going to try to pick out details that are important in a doppelganger fight.

APL and relative CR encounters

A party's APL is

• ((sum of levels)/number of players)-1 for parties of 1-3
• sum/number for parties of 4-5
• (sum/number)+1 for parties of 6.

This is because the number of "tools" available varies by the number of PC's.

CR is directly compared to APL when determining how dangerous an encounter could/should be. CR's less than the party level (effectively everyone fighting a single character of an equal level) is considered Easy. the scale ends at an encounter with CR+3 compared to APL which is considered Epic and has been described as 'at least one player will probably fall'. As you can see, CR isn't linear; it's but actually based on the amount of Exp awarded, so it roughly scales on a negative harmonic progression (wiki link, not important).

One more rule specifically applies, about Gear Adjustment. NPC's have a lower Wealth by Level threshold than PC's and the CR assumes that is followed. If an NPC has no gear (assuming it hampers them) has its CR further reduced by 1. An NPC that has gear equal to a PC has its CR increased by 1.

This alters my previous bullets as so:

• Creatures: 2 CR: 12
• Creatures: 3 CR: 13
• Creatures: 4 CR: 14
• Creatures: 5 CR: 15
• Creatures: 6 CR: 15

The doppelganger concept

Assuming all of this applies directly, CR of an equal copy of the party will always be

• +3 for a party of 2
• +3 for a party of 3
• +4 for a party of 4
• +5 for a party of 5
• +4 for a party of 6

While this assumes combat readiness and the PC's wont have a full regiment of spells ready for the doppels to take, any decrease from loss of spells is equally reflected in the PC's and therefor ends up a null change.

My recommendation

These numbers suggest that this is a bad idea. As you probably guessed, the doppel's have an equal likeliness of winning the fight compared to the PC's. It simply shouldn't be done. There are a couple ways to make this an interesting and engaging fight. You can use one, multiple, or all of them depending on your intent.

• Give the doppelgangers a weakness the party can exploit that the party doesn't have. Make them take 1.5x or double damage from Cold Iron, Silver, Good, or an element. Provide the party some way to divine this and pepper it throughout their last couple fights.
• Give the party a tactical advantage, such as the doppel's aren't fully capable in their adopted bodies yet and can't do a list of things, or always move as though they're on difficult terrain. Have them hampered by the actual environment, or slap a couple Conditions such as Sickened on them.
• Don't play the doppel's as intelligently as your PC's play their characters. Do 'goof up' things like provoke AoO or use low level spells first.

• Finally, consider letting them copy everything except all of their magic items are not magic. That looks like a Headband of Vast Intelligence +4, but on the doppel, it's actually just a fancy sweatband. This would drop their CR by two each resulting in my final encounter difficulty table:

  • Creatures: 2 CR: 10 (APL +1)
  • Creatures: 3 CR: 12 (APL +2)
  • Creatures: 4 CR: 12 (APL +2)
  • Creatures: 5 CR: 13 (APL +3)
  • Creatures: 6 CR: 14 (APL +3)

Answer 2

From this section of the gamemaster's manual we read that:

• For a NPC whose hit dice are class levels the CR is supposed to be HD-1

• there is an easy way to get the CR of a certain number of creatures of the same CR:

  • 1 Creature : CR
  • 2 Creatures : CR +2
  • 3 Creatures : CR +3
  • 4 Creatures : CR +4
  • 6 Creatures : CR +5
  • 8 Creatures : CR +6
  • 12 Creatures : CR +7
  • 16 Creatures : CR +8

A general rule of thumb is that two encounters of CR X together make one encounter of CR X+2

So for example if you have a group of 4 PCs level 10 the encounter would be CR 13 (each opponent is CR 9 and all together it makes a CR 9+4 encounter)

However the problem with this theoretical calculation is that it makes the assumption that your NPCs with class levels will be created with NPC creation rules, which are not the same as for the PCs (they get way less equipment and attribute points). Even if it is not an official rule I usually consider that those differences are worth a +1 to the CR.

But... as you stated those NPCs appear in the same status as the PCs, so maybe they are completely exhausted, maybe not... Difficult to know that in advance, and it could again change the CR.

But! If we go back to the main signification of what CR means it is supposed to indicate how hard will be the encounter, not just be the result of a complex calculation. from this table we can see that a CR+3 corresponds to an "epic" encounter, which means an encounter where the PCs have a significant chance of being all killed. Your encounter is definitely in this range as they have quite exactly 50% chance of TPK.

If your players are experienced Pathfinder players it will be for them an encounter way harder than usual CR+3 encounter as their characters are probably build more efficiently for combat than most of the NPCs.

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That said I don't recommend you at all to do this encounter the way you described it, unless the PCs are very low-level and you expect PCs to die. This is because:

• The more a PC gets levels, the more complex it becomes. You can't reasonably read 4 character sheets of lvl 10 PCs in ten second flat and then be able to play them the way they are supposed to work, even if you are used to improvise with monsters randomly chosen from the book. On top of that some players may have bad handwriting, some value that are not written in the right place...

• If you play the clones right this encounter will very quick and lethal. Most of the characters I created during my player career are able to put a clone of themselves out of combat in one round. It will probably be a contest of "who rolls the best its initiative". The only way for the players to get an ace out of their sleeve is to not tell you about one of their capacities or weakness, hoping you miss it and forget to use it when they know about it and exploit it. You can bet they will try that if it is their only way to win.