Does an enemy lose its Dex bonus to AC if it has a miss chance against me?

Question

If I am invisible, the enemy loses its Dex bonus against me, and has a 50% miss chance.

If I use Displacement, it also has 50% miss chance against me. Does it also lose its Dex bonus against my attacks?
Are these two things linked?

Answer 1

No. Invisibility negates the target's Dex bonus for a different reason.

The effects of invisibility are described here.

One of those effects is, when attacking, a +2 attack bonus, and negating the target's Dex modifier to AC. This doesn't apply against blinded creatures, but you already get those benefits when attacking a blinded creature, so it would be more accurate to say this effect doesn't stack with the effects of blindness.

The implication is that this is the effect of the target being completely unable to see the attacker.

The Dex bonus to AC has a pretty consistent meaning: it's the difficulty of hitting the target because they can dodge. It's negated when the target isn't prepared to respond to the attack (flat-footed, stunned), or isn't free to move (grappled, balancing, climbing), or there's no possible way to see the attack coming (invisibility, blindness).

Now, another effect of invisibility is total concealment, which gives a 50% miss chance against the invisible guy. This also is symmetric with blindness: everything has total concealment from a blind creature.

But what's the effect of being a concealed attacker? See the Combat Modifiers section, which is where concealment is defined, and which has a handy chart of the common conditions that might affect the attacker or defender. There's a line for an invisible attacker, and for a "concealed or invisible" defender, but nothing for a concealed attacker. The clear implication is that there is no benefit to being concealed when attacking.

However, if this is a surprise attack, the target loses their Dex bonus anyway. So we're really talking about a situation where an attacker has total concealment but the target still knows pretty much where they are.

The Displacement spell is a case of that: everyone can still see you, with a margin of error of two feet. Displacement carefully states that it doesn't even give real concealment (for example, you can't use it to hide), and it definitely shouldn't give any of the other benefits of invisibility.