"Dominance: Pay 3 gold to search your deck for a location card with printed cost 2 or lower, and put that card into play. Then shuffle your deck."

The Red Keep has a printed cost "s1." Can it be searched for by Bran the Builder's Legacy?

Wait, d'oh. It probably can't be the target of Bran the Builder's Legacy because it can't be put into play without being in the shadows first. Or can it?

The printed cost is 3 gold. "s" means 2 gold.

If I'm not wrong the printed cost would be 2+1=3, meaning you cannot use Bran the Builder's Legacy on it. Shadows have nothing to do about it.

From the Shadows Rule sheet:

Playing a Card into Shadows
[...]
(Shadow) cards must first be marshalled into Shadows, and then brought into play from Shadows at the appropriate time. (Shadow) cards cannot be marshalled directly into play.

If the value of a (Shadow) card’s “printed cost” must be determined (because of another card effect), the value is determined by adding the cost of playing the card into Shadows (two gold) to the cost of bringing the card out of Shadows (as shown on the card).

The part I put in bold tells you that only marshalling a Shadow card directly to the play area is prohibited. It doesn't say anything about "put into play" effects. So you can use card effects to put Shadow cards directly into play. You just can't pay for it directly during your turn in Marshaling.

The part I italicized tells you how to figure out the printed cost of any Shadow card. "s1" is a printed cost of 2 + 1 = 3.

Just in case you wanted the official rules on any of this....