Based on DanSh0wSt0pper’s solution for the Foe-Hammer achievement, I went for campaign 2, quest 4, section 3. Here, the objective is a 20 willpower door that needs to be boarded, with 3 weapon racks that can be resolved to give an extra +1/+1 to a random character. While the main 20 willpower objective is in play the remaining slots on Sauron's board will be filled with orcs every turn, giving an opportunity to milk kills and/or damage.
Heroes: Aragorn, Arwen and Legolas
2 x Gaining Strength
2 x Lock Shields
1 x Warrior Sword
1 x A good Deed (need to unlock this card by killing enemies with Legolas’ upkeep ability 25 times)
2 x Elven Blade
1 x Guard of the Citadel
2 x Self-preservation
1 x Traffic from Dale
2 x Westfold Outrider
2 x Favor of the Valar
2 x Imladris Caregiver
2 x Imladris Minstrel (BEST CARD OF THE GAME!!!1!1!)
2 x Beorn
2 x Get the Orcs
2 x Erkenbrand
2 x Spear Wall
2 x Gandalf
The idea is to get to the third part of the quest with “Beorn”, “Erkenbrand”, one “Imladris Minstrel” and a 7th ally in play. Every round, Sauron’s side will be filled with “Dol Guldur Goblins” (actually an Orc) giving the opportunity to kill 7 orcs per turn, given that the optional objectives are cleared as soon as possible.
I’m almost certain that damage dealt to an attacking enemy by a defending guarding character doesn’t count for the achievement. For this reason, try as possible to avoid the use of guard; Erkenbrand has guard at the beginning of each turn so you can start attacking with him.
Use the two Gandalf cards to extend the match by selecting the “remove 3 threat” option when he enters play. You can also include the “Favor of the Valar” preparation cards to extend it even more; save the "Gaining Strength" events to be played before the Favor of the Valar in case Sauron has the “Dark Sorcery” treachery in play, which is essentially a counterspell. Also, the 2 willpower cost fate event in this section will also help reduce 3 threat while also damaging all enemies (if combined with a “Get the Orcs” card can kill all the orcs and give a respite turn if needed).
I have two copies of Beorn and Erkenbrand (both unique allies thus one copy at a time can be played) in case I need to replace them due to an accidental death, a discard from a Sauron play, or when I need to play Gandalf with a full board; I remove for example Beorn, remove the 3 Threat, and the next turn after Gandalf flees, replace the free space with the other copy of Beorn.
Give the “Warrior Sword” to Aragorn to set him to 3 attack, and both “A Good Deed” and “Elven Blade” to Legolas to set him to 4 attack. The second “Elven Blade” can either go to Arwen to get her to 2 attack or to the “Imladris Minstrel” in order to give her a little more survivability and 1 attack that can contribute to killing a near-death enemy. Also, it’s important to give that extra health because she becomes target number one from Sauron.
In the topic of Sauron trying to kill the “Imladris Minstrel”, he will eventually play the “Elite Dol Guldur Orc” which have surge and 3 attack (there is only one in his deck), usually when there is no guarding character defending and will kill the non buffed Imladris Minstrel. Keep the second copy at hand to replace her if necessary because this card is mandatory to get to the end of the match.
If the match goes without major mishaps, playing both Gandalfs, playing and triggering both Favors of the Valar, using the 2 willpower fate event and destroying any “Watchful Eyes” Hazard Played by Sauron, you can play for about 36 turns (including the turns wasted in the first two sections of the quest) before failing by reaching 50 threat. This will grant a final kill count of about 150 to 170 orc kills per run and about 550 to 625 damage, plus contributing to several other cumulative achievements.