C – core set
M – Shadows of Mirkwood cycle
M1 – Hunt for Gollum
M2 – Conflict at the Carrock
M3 – Journey to Rhosgobel
M4 – Hills of Emyn Muil
M5 – Dead Marshes
M6 – Return to Mirkwood
K – Khazad-dûm deluxe
D – Dwarrodelf cycle
D1 – Redhorn Gate
D2 – Road to Rivendell
D3 – Watcher in the Water
D4 – Long Dark
D5 – Foundations of Stone
D6 – Shadow and Flame
H – The Hobbit saga
H1 – Over Hill and Under Hill
H2 – On the Doorstep
N – Heirs of Númenor deluxe
S – Against the Shadow cycle
S1 – Steward’s Fear
S2 – Drúadan Forest
S3 – Encounter at Amon Dîn
S4 – Assault on Osgiliath
S5 – Blood of Gondor
S6 – Morgul Vale
Beregond (N) is the strongest hero defender, his highest defence value is supported by the sentinel keyword; there is little else one can do with Beregond but that is to be expected from such a stellar defender. Being Tactics helps to make his defence even better, as should the weapons that can be played on him with a discount.
Defender of Rammas (N) is an ally counterpart to Beregond. Of course he is much, much more fragile and he is not a sentinel but for an ally that costs 2, one gets a lot of defence value.
Winged Guardian (M1) is sentinel and another defender of 4 but it is costly to keep him around. It is good that this Eagle can boost the synergy, and come to join Eagles of the Misty Mountains.
Eagles of the Misty Mountains (M6) get stronger the more Eagles you’ve got, and are able to attach to them; it is a bit riskier to defend than to attack with them, and since a Tactics deck might lack willpower, it may often be they will be exhausted when a chance to strike or block arises.
Defence strength and the number of hit points often determine a successful defender, Ring Mail (D4) boosts both of those attributes. It can only be targeted on Dwarves or Hobbits, however.
Gondorian Shield (S1) may be the most obvious defensive card once you play Tactics and a Gondorian hero. Beregond and Boromir are both excellent choices.
Support of the Eagles (M6) takes a bit of time to prepare, you need an Eagle first to make anything out of it, but it is a very potent way to boost a Tactics hero’s attack or defence.
Stand Together (C) can make defending easier, just as long as you’ve got the card at the right moment and enough defenders to make a good use of it.
Dáin Ironfoot (M6) and Elrohir (D1) have the highest defence value among Leadership heroes. The former will likely be ready when Combat begins as he wants to keep his boost throughout questing. The latter better be ready then because he’s very good at keeping ready once the defending begins.
Errand-rider (N) is a good chump blocker, having 2 hit points for the cost of 1.
Warrior of Lossarnach (S1) and Leadership are the Outlands choices for the defensive boost.
Dúnedain Warning (M2) does for defence what Dúnedain Mark does for attack, again with mobility.
For Gondor! (C) as a defensive card is only good for Gondor.
Frodo Baggins (M2) is a notable Spirit defender, his defence strength of 2 is perhaps enough to claim that; but there is much more to be claimed later.
Aside from being a great willpower boost, Arwen Undómiel (D3) is a great defensive card also, even better in multiplayer, especially when the likes of Elrond, Elrohir (how thematic) or Tactics Boromir are around.
Even though defence is much more of a province to Spirit than attack is, Damrod (N), Elfhelm (M5) and Northern Tracker (C) are worth mentioning even in this category.
Blood of Númenor (N) can become quite a defensive tool in a Gondor deck built around resource acceleration.
Light the Beacons (N) has a Gondor theme to its title and art but it works just as well for any trait, it is costly but very effective once paid for.
Spirit is the least combatant of the four spheres but its hold of the defensive part of it has grown considerably. The newest addition to date is Against the Shadow (S2), the title taken from (or given to) the adventure pack cycle, which allows mono-Spirit decks (printed icons required) to use willpower when defending. One can surely see a way or two to use this card even though mono-decks are still new-born babies.
If one has cards to spare, Protector of Lórien (C) can make any hero a much better defender.
Even without the ability, Harbor Master (S2) is not a useless ally, the cost of 3 for 1 willpower and 2 attack strength. His ability is an intriguing one, certainly not straightforward as it will be futile in a majority of decks. However, a strategy based on resources acceleration and shift of resources is not a bad one, and in such decks the Master can quickly rise into a defender of 3 or 4 (think Théodred, Bifur, secrecy with several copies of Resourceful, but the best card to combo with the Master is surely Horn of Gondor, it can generate several points of defence strength during a single round).
Elrond (D6) and Denethor (C) have the highest defence strength among the Lore heroes, especially worthy of noting since one shadow effect preventing attachment called A Burning Brand.
There are two great candidates among Lore allies for the above attachment. Gildor Inglorion (M4) is stronger of the two in defence value but Haldir of Lórien (M3) is a sentinel.
Gandalf (H1) is especially fit to combat as he doesn't exhaust to quest, and with his great stats he can become some defender.