There are some Grima decks that can work in multiplayer. This is not one of those decks.
The card you most want to see in your opening hand is Gandalf, though obviously the Keys of Orthanc are good too. The idea is to use Grima's ability every round, particularly once you have at least one Isengard Messenger in play. To get the most out of the Messengers, don't play more than one copy Deep Knowledge in a single round, and don't play Saruman during a round when you are playing Deep Knowledge. Once threat gets too high (and it will), reset with Aragorn. This doesn't mean you should stop using Grima or discard Gandalf however, as you should be in a strong enough position to win before you hit 50.
Although it is impossible for this deck to get into secrecy under its own power (and unlikely even if you did try using it in a multiplayer game), the Ithilien Lookouts can be useful for providing a little extra attack and giving you information for using Wingfoot if you haven't drawn Henamarth Riversong (or allow you to use him for his willpower or attack for a round). Gildor Inglorion is a throwback to an earlier version of the deck which included Flame of Anor, as a means of setting it up, but he is useful nonetheless, as he can have the final copy of A Burning Brand (Aragorn and Grima get the first two, along with Protector of Lórien). Lembas is intended for ready Aragorn and Grima in the early game to act as defenders, and healing them in the process. Once Gandalf is set, he takes over as a major defender, especially since, while he can't have a Burning Brand, you can discard the shadow card with his Staff, particularly on any round when Saruman is in play.
For the sideboard, Quickbeam can provide extra cheap attack power, while Secret Paths is valuable early on, since the deck is low on starting , so it may be worth it against quests that start with a high location, or that simply include such locations (some locations in the first few cycles spring to mind, though some of the more difficult recent quests also have them).