Song of Mocking is a rather underrated card. Mostly because it's not really doing anything for you, just making sure the right characters don't die. It definitely has it's uses though. Take an undefended attack and having a shadow failsafe. Pump up Gimli or booming ents. I'm sure there are many more. Of course, most decks could run Vigilant Guard instead, which if I'm correct, works on hero Beorn.

Dunedain Cache, while one of the only reliable ways to make a character ranged, is overcosted. It is however the only way to make a character ranged without a trait requirement etc. That said, if you really want to make a certain character ranged, two resources is probably worth it.

Dunedain Watcher is over-costed. Good, but over-costed. Three resources for one stat isn't good, but if the ability is worth it, than she's playable. And really, your paying for the built-in Hasty Stroke and the ally; which makes it two resources for for one, one, or one. Plus any effects triggering off leaving play like in-sphere Imrahil. She's also the spiritual ancestor of Dunedain Lookout, which is kind of cool.

This card is easily the best (and honestly perhaps the only truly overpowered) Ally ever released. With very few exceptions, you can take practically any deck, cut out a single card, put in a single Treebeard and the deck is probably better overall, even if only slightly. The only real exceptions are janky combo decks that don't intend to actually play the game, so we'll ignore those.

While many high cost characters resemble or even can become heroes themselves, Treebeard is the most efficient cost wise (4 of any sphere) of those kinds of cards. He can boost any deck with Ents by generating resources like a hero and, if you're not using any other Ents in your deck, he still finds use with them by having a built in Unexpected Courage every other turn ... meaning he can hit with his full 4 damage right after doing what he does best, tanking.

Boromir is OP. Period. Even without the Blood/Fire/Steward shenanigans he's incredible. With the amount of threat reduction available at this point in the game's life, you could build a deck entirely devoted to threat reduction to keep that Boromir player up and running. There's also the deck idea of setting up the other players to do their thing and then die before revealing encounter cards. Boromir fits right in to it. Honestly, there is no limit to the power of Boromir (and I don't want him errata'd!).