While fighting defensively with Combat Expertise, 19.

Round 75 (12:07:30)

If you choose to take a -7 penalty to hit I'm going to start making you actually roll for that.

The shadow rolls 13 on the d20 and adds four, 17. Swing and a miss.

Round 75 (12:07:30)

No more sneak attack, but now Vencarlo can make two attacks in a round.

He has a +15/+10 bonus to hit with his rapier, or rather +8/+3. Neither attack hits.

Round 76 (12:07:36)

Shadow rolls a 12 on the die, +4 is 16, but Vencarlo dodges. 19 touch AC is pretty much as high as it gets, in Korvosa.

Round 76 (12:07:36)

On this keen rapier, an 18 and 17 both threaten critical hits! Though only the first confirms. Together they deal... 12 points of damage, reducing old man Mauro Silanus to 0 HP!

If you didn't want to go to the Abyss, you should have tried harder not to get eaten by shadows.

Hey, Blackjack, give me a Perception check.

Rolled a 20. So. 19.

What's your flat-footed AC against touch attacks?

10.

Round 76 (12:07:36)

Take a point of strength damage.

Round 77 (12:07:42)

Vencarlo wheels to face the shadow that rushed him and strikes at it twice. Both miss.

Round 78 (12:07:48)

Sometimes shadows roll 17s, too. Does a 21 hit your touch AC?

Yes.

Take six points of strength damage.

Round 78 (12:07:48)

Vencarlo has 2 strength left. His sword and leather armor make for a heavy load; his armor class drops by 3.

He attacks twice. Two critical threats, both confirm. With his strength penalty, they do 4 damage and 5.

Nine points of damage out of the shadow's 19 HP.

Round 79 (12:07:54)

A 17 hits, for 1 point of damage.

Round 79 (12:07:54)

That puts him above his heavy load. Vencarlo falls prone in the mud.

He can still attack, albeit with a -4 penalty.

Both strikes hit, for 5 combined damage.

Round 80 (12:08:00)

Even prone and encumbered, he's still Vencarlo fucking Orisini.

A 6 to hit won't touch him.

Round 80 (12:08:00)

Vencarlo lands an attack for 2 points of damage. In three more damage the shadow will die and Blackjack can drag himself away.

Round 81 (12:08:06)

It was close.

You fought hard.

But take 5 points of strength damage.

These things are CR 3??

Ostensibly.

If a dex-based fighter like Vencarlo can fight two shadows one at a time, roll four critical hits[1], and still lose, what hope is there for the rest of us?

Cressida Kroft has a touch AC of 10. The moment a shadow tags her she'll stop qualifying for Power Attack and do even less damage than Vencarlo did. She can't even take more hits than Vencarlo did; her Strength is 5 higher but she's wearing fifty more pounds of equipment she can't quickly doff. When her strength drops from 14 to 5 she'll be immobilized in her armor.

The Korvosan Guard has emergency wands of mage armor, distributed to their handful of wizards, but that won't bring anyone's AC higher than Vencarlo's was without it.

If they had wands of shield as well, for 10 glorious rounds she could have 18 touch AC. Still lower than Vencarlo's was. If they put those spells on a character with as high dexterity as Vencarlo without his belt, and that character is aware of the shadow and ready for it, and fighting defensively, the shadow would still land attacks when it rolls 18, 19, or 20. If two shadows attack at once, they hit on 16 and 17 too. And if a shadow charges from hiding, they hit on a 12. (On a 10, if the shadow charges into the flanks of an ongoing fight.)

It's certainly possible to get your touch AC higher than this, and even your flat-footed touch AC. But not scalably and not in a hurry. You have to tailor your build for it, have expensive items, or be a monster from the Bestiary.

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1. The reader RationalMoron points out that as incorporeal undead shadows should be immune to critical hits and Sneak Attack. ↩