Here is a multiplayer support deck I have been trying out and updating after running an earlier prototype of it at a LotR meetup. These three heroes don't seem to be among the most popular in the game right now, which reduces competition between this deck and others for unique cards. Elfhelm's buffing is great, his defense and attack boosts are especially appreciated, one extra point can make a difference. Buffing everyone is what this deck is designed to do.
In the first round or soon after we want to get Master of the Forge onto the table, failing that Gléowine or King Under the Mountain do nicely as well. Once the master is fetching our attachments, we are well under way. Narvi's Belt is for Bifur, so we can pay for those off-sphere mounts. You can give mounts to other players, buff their heroes even more with those Dunedain attachments while using Rune-master to shift resources to their heroes, use Ranger Provisions on someone, or heal someone with Dúnedain Remedy. Putting The Day's Rising on Erkenbrand is something we ought to do first though, and send those resources over to Bifur with his action. At some point we will likely use either Faramir or For Gondor! to provide global buffing. With our archers, we can also help out in combat where needed and maybe take on an enemy ourselves. Most of the allies we will be sending to the quest are scouts and Elfhelm is a scout himself, so we can use Scouting Party for a bit of a power questing push. The Evening Star also helps prevent location lock.
This deck offers good assistance to other players, and there are a ton of possibilities as far as alternative attachments, use whatever your group might need. Cram, Miruvor, and The Long Defeat are great for other players though. To summarize, this is a fun deck that contributes to the game by empowering the other players.