On any character other than Theoden, King's Mail is functionally identical to Armor, with 1 extra twilight cost. On Theoden himself, the card provides additional protection, shielding him from effects such as Hate; Ulaire Enquea, Lieutenant of Morgul or You're a Liar and a Thief.

King's Mail helps Theoden to become a very tough companion, especially when combined with Herugrim and/or Hearken to Me. It can however be viewed as more a luxury than a necessity, as it is likely to put a well-equipped Theoden at risk of being punished by effects such as that of Grima, Wormtongue or Lying Counsel. This is especially true with The Two Towers versions of Theoden, as he is weaker than his The Return of the King versions.

King's Mail has a fairly hefty drawback of preventing the Free People's player from wounding him, even if they want to. Theoden cannot take archery wounds or threat wounds while bearing this possession, which forces the Free Peoples player to put those wounds on other characters (Such as the Ring-bearer). In cases such as these, it may be wise to play King's Mail on a different companion (Or transfer it) to prevent this. Or discard it in skirmish with Charged Headlong or Unyielding. This issue is resolved with the release of the Throne of the Golden Hall in set 17, which allows Theoden to exert to prevent another character's wound, essentially achieving the same effect.

• Direct wounding (Hate; Ulaire Enquea, Lieutenant of Morgul; Horribly Strong; A Host Avails Little)
• Damage Bonuses (Lurtz's Battle Cry; Cave Troll's Hammer; Uruk Vanguard)
• Mid-skirmish wounding (Red Wrath, Whirling Strike, Black Gate Sentry)

• Archery and Threats