While Watch Tower is in the staging area, it gains:"Forced: When a Raider enemy enters play, add 1 resource to it."

Shadow: If this attack destroys an ally, add resources to a Raider enemy in play equal to that character's printed resource cost.

Each Raider enemy with at least 1 resource on it is immune to player events.

Forced: At the beginning of the resource phase, add 1 resource to each Raider enemy in play.

So it stood, until after the second arising of Sauron, which now approached. Umbar fell under the dominion of his servants, and the memorial of his humiliation was thrown down.
–The Return of the King

When faced with the option to travel, if Streets of Umbar is in the staging area, the players must either travel to a location named Streets of Umbar or add 2 resources to a Raider enemy in play.

Shadow: If attacking enemy is a Raider deal it an additional shadow card for each resource token on it, to a maximum of 3 additional shadow cards.

X is the highest number of resources on a Raider enemy in play.

Travel: Search the encounter deck and discard pile for a Corsair enemy and add it to the staging area. Shuffle the encounter deck.

While Umbar Harbor is the active location, Corsair enemies get +2

Shadow: If attacking enemy is a Raider move 1 resource from a hero you control to attacking enemy.

While Umbar Bridge is in the staging area, cancel the first X progress that would be placed on the current quest each round, where X is the highest number of resources on a Raider enemy in play.

Travel: Reduce the engagement cost of each Corsair enemy to 0 until the end of the round.