I played a game last Saturday with my friends in person (4 player). Board had Cultist and Transmute without anything to really counter the Cultist... other than the Transmute. Now, I've heard people suggest Transmute is great with Ruins before, but seeing is believing. Three of us went for Cultist while the fourth opened Potion/something. We ended up clogged up with Ruins while he was able to quickly nab a Duchy lead. By the time we had all caught on to the idea and started doing the same, he had already won, piling out Duchy, Estate and Fishing Village. (On that note, Cultist is a great Transmute target in the same situation... gain a Duchy, draw 3 cards)
I love that previously 'useless' cards are starting to see some great combos in Dark Ages.