I was playing DE against Dwarfs with my wife last night. She had the following cards in her Battlefield:

1 Troll Slayers ( Battlefield. This unit gains 2 power while you have at least two developments in this zone )
1 Serpent Slayer ( While you have at least three developments in this zone, this unit deals +X damage in combat. X is the number of developments in this zone )
4 developments

Because of the developments, Troll Slayer has power of 3 and Serpent Slayer deals damage of 6. Quite a package!

She attacked my Quest Zone, where I had:

1 Harpies
1 Mortella
3 developments

Now, I wanted to play Take Captive! (Action: Take control of target attacking unit until the end of the turn. Move it to the attacked zone, declared as a defender ) to move 1 of the Dwarf Units into my Quest zone in order to help with the defense. Since we were not sure about is how the move will affect the units with respect to the new zone location and the number of developments, I did not play Captive in the end, so know wanted to check here how it works. So our questions are:

1. When moving units that have a contingency on developments into an opponent's zone, do they consider the developments in the new zone, i.e. from the development of the opponent?

2. Assuming that this is the case, is the following play correct?

A. If I move Troll Slayer, he is not in a Battlefield anymore, so he will not gain the extra 2 powers and is left with 1 power for defense.

B. If I move Serpent Slayer, he will now deal 5 damage (2 plus 3 developments in DE Quest Zone)

Thanks!

You got it right. In both cases, it is a constant effect. So you have to continuously check if the condition is still met. The Troll Slayers' effect only works in the battlefield, so when you move them to a kingdom or quest zone, they lose their two extra power. If you had moved them to your battlefield, and you had at least two developments there, they would have kept them. The Serpent Slayer's effect isn't zone-specific, so when he is in combat and gets to deal combat damage, you check how many developments are in the zone he's in, and adjust his damage accordingly.

It would be different if you had been playing against Empire and a unit had gotten +X power from Shrine to Taal. That effect lasts until end of turn, and when it triggers it looks at the number of developments in that zone at that time. When you move the unit later during that turn, or play an additional development into its zone, X doesn't change.

Thanks Mallumo for your reply, this is most helpful!