You are playing Nightmare mode.

Arrows thick as the rain came whistling over the battlements, and fell clinking and glancing on the stones. Some found a mark. The assault on Helm's Deep had begun...
–The Two Towers

Begin with the standard quest deck and encounter deck for the Helm's Deep scenario.

Remove the following cards, in the specified quantities, from the standard encounter deck:

1x Isengard Uruk

3x Uruk-hai Fighter

3x Wild Hillman

3x The Hornburg

1x Deeping Wall

2x Postern Door

2x Reckless Hate

Then, shuffle the encounter cards in this Nightmare Deck into the remainder of the standard Helm's Deep encounter deck.

Finally, flip this setup card over and place it next to the quest deck. Its effect remains active throughout the game, which is now ready to begin.