The problem is that
Beneath the Mountains makes you play a
weapon
from discard or from hand. And the rules state that if you use an effect to play a card from discard pile, that card must be there first and must be played. Alike
They Are Coming, which can't just discard 3 to merely cycle (if you don't have a Goblin).
Realm of Dwarrowdelf is a good option too. Besides ditching your deck, makes Gimli really hard to kill, which is awesome with both
Bearer of Grudges and
Feared Axeman.
EDIT: Rule explanation corrected above. That rule includes playing from hand. Actions that play cards from hand need too that card to be already on that location. For example,
Bilbo BotB needs to have a
tale in hand to use his regroup skill, you cannot use it just to add burdens (for
TSC) in absense of
tales in hand that can be played (
TABA doesn't count if you have another copy in play, due to its uniqueness).