The synergy with Vilya was probably the first thing everyone noticed when Gandalf was first spoiled many moons ago. This deck updates that formula, by adding Arwen to the mix to get it rolling even faster. This comes at a whopping 36 threat but powers up much faster than the Glorfindel version. The deck is vulnerable early game on high threat quests and to early attacks by beaters, but can do just about everything (quest, defend, attack, treachery & location control, healing, self-threat control) once it gets past that hurdle. Works particularly well with a Silvan deck in the mix, despite losing Haldir/Galadriel.
Whilst this deck likes to use Steward on itself to get set up asap (despite Vilya cheating everything into play), it can give away resources and cards via Arwen and Gandalf's Staff (though I prefer the shadow discard most of the time, the flexibility allows you to adapt to the situation) to make up for it. Also everyone loves the Elrond healing buff, and in big multiplayer battles excess resources from Steward can help spam healing too.
It draws at a phenomenal rate (guaranteed Expert Treasure Hunters, Elven Light, Daeron's Runes, Galdor, Legolas, plenty of cards that work as pseudo-draw by playing off the top of the deck in various phases) and a 2nd Will of the West wouldn't go amiss. This means after the initial threat issue you can actually drop quite fast with Elrond's Counsel. With another player sporting Galadriel, I finished Siege of Annuminas on 32 Threat.
It's 56 cards but it always sheds some allies based on what other decks are using as Heroes, you can also bulk out the Allies with other heavyweights such as Glorfindel, Landroval, Treebeard. I had Imladris in there but found myself always using it as a chump, thanks to pipe. Gleowine is an option for more consistency but it draws fine. A second Steed could also work. Hour of Wrath can also be an interesting include to put Gandalf into god-Mode, but has to be played via Pipe-Vilya. Basically sideboard is every 4-5 cost Ally I own (I don't have Glorfindel or Treebeard) & Hour of Wrath.
Works best in tough multiplayer quests where it can dominate after the initial rounds. Can solo, but depends on quest.