So I have built two Secrecy Decks
One is based around the Twins, getting lots of resources via Resourceful & Steward of Gondor, Sneak attacks for the Gandalfs and a few more expensive allies in there and Out of the Wild to get them out cheaply
The Second is Aragorn & Glorfindel Both the latter versions. This one concentrates on threat reduction and treachery/Shadow control and hopefully gets out the Zigil Miner & the Stargazer to increase resource production. Found a nice synergy with Song of Earendil for the other deck, basically get this attachment out and protect the other deck from threat increase at each end phase. With it's own Gandalfs being used to reduce threat if need be. Otherwise you simply reduce your own threat or if it completely blows out let it hit the 40s then use Aragorn to reset to 17.
So the decks seem to play really well.
Except The first quest Passage through Mirkwood is kicking the collective asses of these 4 Heroes. Just Bizarre.
It might be a bad quest to try against as shadow effects are good at stripping attachments, and the treacheries can make you lose all your events.
I will keep fine tuning and report back!